If this happens only in Safari (images are fine when viewed in other browsers), then this is a bug in Safari/WebKit. The bug can cause odd behavior with image changes on certain websites visited in Safari.
Technical explanation (skip if you don't care about the gory details)
This is a known issue with WebKit and the "beforeload" event listener that we and other ad blockers use to allow us to block content from loading in WebKit. The "beforeload" listener has been deprecated in WebKit in favor of the content blocking API, which AdBlock supports. That means it is likely WebKit and Apple have no plans to fix it.
Here are some links that describe the bug:
If you are a website owner experiencing this issue
The second bug report, which is still open, has an example web page that shows the buggy behavior in Safari. We suggest you review your use of offsetWidth on images and try to avoid it, if possible. You may be able to get more information from the bug reports and by asking for help in the Apple Safari or Webkit forums.
If you experience this issue while visiting a website
Enable Safari Content Blocking in AdBlock's options, GENERAL tab. This should resolve the problem. (Not sure what Safari Content Blocking is?)