I haven't seen the Snapchat codebase at all, but my knee-jerk suspicion is use of an off-the-shelf image cache. Caching images on the device is basically a uni

I haven't seen the Snapchat codebase at all, but my knee-jerk suspicion is use of an off-the-shelf image cache. Caching images on the device is basically a universal problem for mobile apps. It improves responsiveness and prevents unnecessary network usage. As such, there are open source libs that do all the boring heavy lifting for you. Most images caches also don't hold sensitive images, nor do they really expire. In this case, you may have deleted the database row around the post, but the image cache still has the image on-disk.