Just a quick check: I haven't found deleted images until and incl. #1532
#1531 was the first where I noticed missing images.
My guess would that it is an 8chan algo that deletes the images to save space ….
#1531 is almost 6 days ago or approx 300 threads down in the catalog list without new posts ….
If it's an algo, then I'd expect the first missing images to also appear in #1532 next.
Those images from older breads that are not deleted, might have been reposted in later breads.