This picture frame is designed to fit any rectangular sized picture and requires no supports.

In PrusaSlicer:
Scale the X and Y dimensions for the back plate to the dimensions of your picture (e.g., 150mm x 100mm)
Then scale the length of the side pieces to the dimensions of the back plate - 4.4 mm (e.g., 150 - 4.4 = 145.6mm and 100 - 4.4 = 95.6mm)

Corner pieces and the hanging hooks are printed with the back down.
No support needed. There is an integrated support for the corner pieces.
Side pieces are printed front side down, so that you can have a nice textured surface for the front of the frame.

Use a dab of superglue to attach the corners to the frame.