A simple self-standing picture frame., knocked up in a few moments using Fusion 360.

You'll need to two of the corners with the feet for the bottom and then two of the bare corners for the top. The sides can then be scaled along their length to match the size of the picture you wish to frame. All pieces should print without support, but I put a brim around to prevent warping depending on the filament used.

I'd suggest putting a piece of board in with the photo, and sand each of the ends until smooth and then super-glue them together around the frame.

The quite dark gold filament I used for the frame for a picture of my kids (shown here) almost came out like bamboo.