I think the corrupt stuff started happening after they updated files/coding on the site. As near as I could tell, it is the thumbnails that are being labeled as corrupt. when you use the 'add to game' option, the thumbnails aren't being downloaded by the launcher so the S3P shows up fine in Custard.
Here is a screenshot of the most recent time this happened to me. I'm positive that the easel is from a photograph my sim took of one of your paintings on that mega-painting lot. I'm going to send my sim back to collect those and make another S3P to double check this.

Anyway, I love the idea of adding photographs as decor since they are much less expensive, and we can be more creative with them, than the paintings available in the game. I think I'm going to try some of your ideas for seasonal photos next!