Ideas
Here's an update on my issue with a black graduation photo. From my understanding, most people here have white graduation photos, is that correct? Since mine is black I might have a different issue than what other people in this thread have.
Anyway, I managed to find the graduation photo in its original state, in a backup from 2022. I'm quite sure that it hasn't been black ever since then, but I don't know when it happened and couldn't find any newer backups with it on its original state. My hypothesis is that the graduation photo lost the connection to the sim, maybe when he moved out of that house, or because of some bug later. I've had this happening with other items that sims own, for example a cloning machine that one of my sims built.
Yes, I think this is a separate issue (since the main problem people are reporting, and that I'm having, is a white picture rather than a black picture). BUT, I think both problems are related. In both cases, I would guess that the issue is that the picture object is losing the link to the Sim or texture in question, and therefore is turning white or black. Different causes of the loss of connection, or perhaps different types of interruption of the chain of instructions that need to happen in the game code, cause the different effects (black, white, or in less frequent cases a corrupted image file).
If you read my earlier analysis comments, I noted that for the pictures in my save, when the objects spawn they are initially black, then turn white. Before this error began, they would spawn black, and then put in the picture of the Sim (i.e., the texture). So perhaps in your case, you are getting to the first step of this (black picture), but you aren't then progressing to the next step (replace black with correct texture).
I have no idea how the game code works; this is all just speculation based on observation and reading a lot of comments. But I think it's at least a possibility.