If you are wondering what this Instructable offers you other than re-creating my picture, this Instructable covers in-depth all of the basics below.
What Basics I Will Cover:
-Create a workspace and keep it organized
-Curves Tool (best tool Photoshop offers)
-Shadows (Burn Tool)
For this Instructable, I will be assuming that you either have Photoshop or any other photo-manipulation software. I have never used anything other than Photoshop and MS Paint (a long time ago), but I can only assume that most of the tools in the free online photo-manipulation programs.
1 - Computer, I am using a Mac (you don't have to use a Mac)
1 - Photo-manipulation program, I'm using Photoshop CS5 (this works with lower versions)
1 - A basic understanding of layers and tools
1 - Time, this took me 3 hours, but I took screenshots and wrote this Instructable too
(1 to a lot) - Source Pictures
Cost: Free if you have all of the above.
Step 1: Source Pictures
Building - Find a building with at least two sides showing, so that you can make an interesting looking banner that isn't just a single flat piece of paper/plastic/what ever you want to make the banner material out of.
Banner - I chose the Instructables robot, but you can chose a logo from a business, internet site, or even a picture.
Those two sources are all that you need to create a banner over a building, now if you want to make the picture more detailed, you will need source pics (Ex: rope, textures for the banner, etc.). For the basic idea, I am only going to use two source pictures. Once you get this down, you can elaborate with added extras.
Step 2: Getting Started - Work Space
Creating the space - For a perfect fit, I usually copy the source image that I am going to use, then go into the File>New> (should have the dimensions of the copied image) and change the resolution to 300, then click OK (I usually don't save these, so I wouldn't bother naming them). If you are concerned about the amount of space it takes up, just remember you can convert it into a jpeg later once you are completely finished and erase the files used to create the image. the 300 resolution will allow you to blow the image up to a easy to view size later.
I prefer to open a new Photoshop page for each source image, so that I can make adjustments to them without being distracted by the other layers.
Important Tools - The tools that I will use the most are the Marquee Tool (box with dotted lines), Quick Select Tool (paint brush with dotted lines where it is painting), Eraser (I hope you know what this one looks like, an eraser), Dodge (looks like a pin), Burn (looks like a hand pinching something). The other tools I will use aren't in the tool box on the side, they are in the tabs up at the top.
If you do not know what these tools do, I would advise you to google it in order to see exactly what it is each of these tools does.
Step 3: Prepare the Images
What does curves do? Curves allows the user to increase and decrease shadows and highlights in their pictures. Curves gives the user a diagonal line on top of a chart with the amount of shadows and highlights used. Shadows are on the left of the box, highlights are on the right, if you move the line below the middle diagonal, it increases darkness, if you move it above the line, it increases the light of the image. I've included pictures of the Curves tool in action.
First Picture: This picture shows the building and the curve tool before I have made any changes, notice the line in the curves tool window is diagonal. The most common shape of that diagonal line is an S curve, below the line on the left side, and above the line on the right side, this increases the darkness of the shadows while lightening up the light parts of the photo.
Second Picture: This picture is post S curve on the Curves tool, as you can see, I added depth to the picture easily. Be careful with the curves tool, if you bend the diagonal line too much your picture will become unrealistic. Sometimes it is the desired effect, but not in this Instructable.
Step 4: Combining Images
With the robot selected, copy the image (Command+C for Macs, Ctrl+C on PC) and paste it into the picture with the building (Command+V for Macs, Ctrl+V for PC). When you paste the image, it should create a new layer above the layer you have selected. (Second Picture)
Then select the robot layer and grab your Move Tool (looks like an arrow, Shortcut: V), move your mouse over the corner of the picture until you get a set of arrows that allows you to rotate the robot. (Third Picture)
Step 5: Realistic Perspective
This is where perspective transformations come into play, but first we need to break down the robot layer so that we can shift each part of it.
Breaking the robot down - To do this, we need to reduce the layer's opacity in order to see the edges of the building behind it, I do this by using the opacity slide on the Layers box (I marked it on the picture). Once it is slightly see-through, grab the Marquee Tool and select the side of the robot that is in the direct sunlight (First Picture).
Once selected, right click and choose "Layer Via Copy" just so you will always have the original robot just in case you make a mistake or want to try again once you finish. Name this layer "Robot Right Side".
Before you select the other sides of the robot, RESELECT THE ORIGINAL ROBOT. If you don't you may select a blank space, or the building. It all depends on what layer you have selected. Now select the robot on the other sides of the building (two more sides). Name them "Robot Middle" and "Robot Left Side", or whatever you want to name it, you might as well name the other layers too. Finished selections are displayed in Second Picture.
Warping the sections of the robot - Before starting the transformations, you may want to increase the opacity of the robot parts as well as hide the original robot picture. To increase the opacity, select the robot layers and increase the opacity to around 80% or so. If you don't know how to hide layers, all you have to do is select the box to the left of each layer (it has an Eye icon in it). (Third Picture)
OK, to warp the robot, select the layer you want to work with first, then click Edit>Transform>Perspective. You may want to mess around in this for a little while, remember if you make a mistake, just click Command+Z to undo. If you mess up multiple steps (since this only goes back one step), go to Edit>Step Backward (or Command+alt/option+Z for Macs). Picture Four has the first layer in the correct perspective, there is no real science to transformation. Just make sure that when you look at the entire picture that the robot looks like it is sitting flush with the building.
Step 6: Shadows (Part 1)
Burn Tool - Use the burn tool to create shadows on an object, this is also used to enhance shadows that already exists on an image (such as creases on a face, adding shadows from sunlight to people you Photoshopped into an image, etc)
Color Overlay - I prefer to use this when I want to darken an entire image (such as the banner on the left side of the building).
Now to add shadows to the banner using Color Overlay - Select the "Robot Left Side" layer and right click it to bring up a menu, then click on "Blending Options" in the menu. Select the "Color Overlay" tab in the menu. Then click the color box and change it to black, and slide the opacity down to around 30%. Do the same thing for the middle part of the robot banner, except change opacity to around 20-25% so that it looks like it has a little more light than the back of the building. (First Picture)
You should come out with a banner that looks like it is on the side of the building. You can always adjust the pieces of the banner with the Move Tool if the perspective tool left your image a little too stretched, I made those adjustments as I was editing other parts of the banner. The robot after shadows is the Second Picture.
You can call it quits here, or you can continue with the details of the picture, such as bringing the street lights and signs in front of the Instructables Robot, and adding creases and stretch marks on the banner.
Step 7: Shadows (Part 2)
Before we go off and burn the banner, we need to make sure none of the banner's layers are overlapping, if they overlap, they will be brighter than the surrounding banner, so just use the Marquee Tool and erase any overlaps. Then create a new Group, this is the button with the folder icon on the bottom of the Layers menu. Name the something like... "Old Robot" then drag and drop the 3 separate robot layers into the folder along with the original robot.
Once in the folder, right click the folder and select Duplicate Group and name it something like "New Robot". Once you have a new group, open it up and delete the original robot layer in the "New Robot" group only since you have the other original robot in the "Old Robot" group. Select all the layers that are left in the group by left clicking the top layer, then hold shift and left click the bottom layer. This selects all the layers between your two selected layers.
Before you merge all three layers into one, make sure that you change the opacity of the layers to something you like, I am going for a thick plastic look, so I set mine to about 92%. Once all the layers are selected, right click and select "Merge Layers" to bring all 3 parts into one layer. Merging layers makes it impossible to increase the opacity of the layer, so make sure you have it at what you want, or you can set opacity to 100% and change it after you merge.
Before you change the shadows on your single layer Robot, Hide the "Old Robot" group by selecting the eye that is to the left of the layer.
Now for the actual Shadows!
Before you start burning your picture, reduce the opacity of the robot layer so that you can see the protrusions of the building. Look for sharp protruding corners, and ledges, these will cause shadows when they push into a banner. Once you get a good layout of the building, grab your burn tool and set the exposure to around 15% or so and color where shadows would be. If you are using the robot picture, you will notice it does nothing to the white parts. Since you can't use the burn on white, you will have to use the Paint Brush (Shortcut: B).
To make shadows with the brush, select the brush with the fuzzy exterior (I couldn't think of a more descriptive word). Change the color to Black and set opacity to around 20%. Next, create a new layer in the "New Robot" group called Shadows, then make some shadows.
Step 8: Replacing Objects
Once you have all of the light poles and signs in new layers and you have erased the building from around them, move all of the layers above the "New Robot" group and see how it looks. If you notice sharp edges, you can always go over it with the Blur Tool (looks like a drop of water). Now you can say you are finished, or you can add other objects to the picture, or add a filter over everything for a different look.
Step 9: Finished Product
Feel free to post pictures that you make using this technique in the comments section.