Designed this for my lithophanes, hope you like it. Do to a lack of forethought I used a random pic for my first lithophane and it was not a standard dimension so you need to crop the photo to 1024x1244. Also the litho was design using itslitho.com with these settings: Shape- Arc, Height- 120mm, Angle- 60 deg. Max thickness 3.2. The finished litho should slide right in and the lid will snap on, Add any led light with self-adhesive pad to the back wall.
One of my test prints of this began to warp a little so I added some internal structure to help prevent this from happening.