I cropped the photo, but how did the original appear in the preview?

Question

Image processing

Good afternoon. When placing an ad on several boards, I noticed that on one of the sites, when adding photos, their preview looks like the original photo. After publishing the ad, I checked, everything is in order, only the cut out part is displayed. But how is this even possible? Is there "some" memory? The photo was processed with FastStone Image Viewer. Previously, I sometimes noticed something like this on a computer, it looked something like this:
1)
2)
3)
Ie . there was a file "1", I cut out a piece from it - "2", but the thumbnail of the picture on the computer looks like on "3". Until now, there are several images on the PC that look so deceptive.

Answer 1

stackoverflow.com/questions/10349622/extract-thumb...
short description of your "some memory" (thumbnail) - in answer marked as solution

Answer 2

https://thumbsviewer.github.io/