I can confirm this bug exists in a Base Game Only save, no cc/mods, never used. I have never modified or even been in the Pancake's house in this save before.
Easily replicated via the camera phone (no skill in photography) and the Barely Better Digital Camera. Have Bob Pancake stand in the living room, choose "Take Photo" from the phone menu.
Also tested with Eliza Pancake and phone camera, then had a sim with limited level 1 skill in photography (30%) visit the home and replicated with the Barely Better Digital Camera.
All of the photos will have these phantom curtains. They only appear in the photos - not in Live mode nor in Build mode, so there is no way to get them out of the picture. There is nothing in the room above that could account for these, either. As shown in the photos from @MapleSimmer they appear on the walls at the front of the house and the exterior side wall - none are along the interior side or back wall. They also don't all line up with the windows or existing curtains.
Front wall:
Exterior side wall:
