Step 1: Download and Install Brushes
If you don't have Gimp already installed, download it here , then follow this wiki on how to install it. You will also need the blood , cracks , and halloween brushes. Once downloaded, they'll need to be installed by copying and pasting them to your gimp brushes folder. It will might be different on your computer, but I pasted them to C:/Program Files/Gimp 2.0/share/gimp/2.0/brushes. For more info on installing gimp brushes, visit here .
Step 2: Cracks and Blood
Locate and right-click image in your file browser, then click "Edit with Gimp". Alternately, open Gimp and click File>Open, then browse for your image and click OK.
Use the brush tool to "stamp" different cracks, blood puddles, splats or smears on different surfaces. Adjust the size and opacity in the brush settings below the toolbox. Try to make it appear to have had a struggle from the bed to the closet, window, or under the bed. Use different sized brushes so it doesn't look repetitive. More cracks equal more age. More blood equals more rage. Change your primary color to dark red when you want to use the blood brushes. To change the brush angle, rotate the image with Image>Transform>Rotate "X" degrees clockwise/counterclockwise. After stamp down angled brushes, switch the image back to normal rotation by click Image>Transform>Rotate, and rotating it back, opposite of the first time.
Step 3: Night Lighting and Glowing Lamp/Moon/Flashlight
Since your room was probably not taken at night, we can make it appear so and add a glowing lamp or moon for effect. If you don't have a window or lamp in your scene, you can simulate a flashlight (or torch) beam instead. Take note, each method (lamp, moon, or flashlight beam) is in a different section. I'll number them for ease.
1. Lamp light
To have a lamp light your scene, begin by using the lasso tool to select the general area around the lamp that you want lit. Refer to photos for an example. For realism, feather the selection with Select>Feather, then adjust the feather amount to 25 to 50, depending on how sharp you want the light to be. I used 30. Click OK, then proceed to give the lamp a yellowish color by clicking Colors>Color Balance, and adjusting the bottom yellow slider to a level that is realistically yellow, but not too yellow. -40 seemed good for mine, but it'll be different for every picture. This yellowing step is optional by the way, but it might be a good idea because otherwise, it may look too white against the soon-to-be dark background. Once you've applied your changes, invert the selection, (Select>Invert), then adjust the brightness and contrast (Colors>Brightness-Contrast...) to make it appear night. I brought the brightness all the way down, and adjusted the contrast up a bit. Now if you your light looks a little too yellow against the dark background, (like mine was), invert the selection again, and bring down the brightness with Colors>Brightness-Contrast.... Click Select>None.
2. Moon light
To have a moon glowing in a window, click Select>All then bring the Brightness and contrast down with Colors>Brightness-Contrast... to make the time appear to be night. Next, give the room a blueish hue by clicking Colors>Color Balance, and adjusting the bottom slider to blue at whatever intensity level that gives it a moon-like tint. Mine was around 60. If you have a bright patch of sky outside of your window where you want to add the moon, (like I did), select a blackish blue color as your primary color, and fill it in with the bucket tool. Now to add the moon, create a circular selection with the eclipse select tool where you want the moon to be, feather it to a value of 20 (Select>Feather), and fill it in with white by using the bucket tool. Click Select>None to deselect the moon.
To illuminate an area as if a flashlight (or torch) is being pointed at it, first select the desired area to be lit with the eclipse select tool, then feather it to as much as you want the beam to be softened (Select>Feather). The higher the feather value, the softer the beam. Invert the selection, then bring down the brightness and contrast by clicking Colors>Brightness-Contrast.... Invert again so you can edit what color and/or how bright the spot is. Do that in Colors>Brightness-Contrast..., or Colors>Color Balance. Click Select>None.
Step 4: Saving
When you're done editing everything, in addition to exporting it as a normal picture, I'd also advice you to save the project file in case you notice something later that you want to change without having to start all over. Save as a project file by clicking File>Save As..., and giving it a ".xcf" file extension without the quotes. Save as a picture file by clicking File>Save As..., and giving it a ".jpg" file extension without the quotes.
Be sure to share yours in the comments section below. Have fun, and happy Halloween.