What is 3Dprinting lithopane? check this instructable https://www.instructables.com/id/3D-Printed-Photogr... Thanks to @amandaghassaei , now we can turn 2D picture into 3D lithopane by using customizer, online!
Step 1: Open in Customizer
Step 2: Choose Picture
Click "Choose file" to upload a picture
Step 3: Invert Colors
Click the invert colors checkbox.
Step 4: Choose Picture Shape
Choose square picture shape, standard is 4:3 aspect ratio and HD Wide is 16:9.
Step 5: Create It
Adjust the value of Layer height and Number of Layers to obtain the best results.
Click "create thing" button.
Step 6: Set a Name and Publish
you'd better don't click on "publish new thing" checkbox if you don't want publish it to public.
Step 7: Check Progress
Click "Go to my Queue"
Step 8: Wait for Completion
Customizer will processing your project online.
Step 9: Done!
Click "View Thing" button.
Step 10: Download & 3Dprint
We can see "This thing is not yet public. You must publish this thing for everyone to see it"
Click “Download this Thing” button and download all files.
Now we get a STL file, print it as usual.