Icons in browser thumbnails

[ACEkin]

I wonder if someone could direct me to some part of the documentation that may explain the tiny icons I see on some thumbnails, like those marked with red arrows in the attached image?

Thank you,

Cemal

[xnview]

the file has a embedded thumbnail

[ACEkin]

Thank you. I thought it was something like that and opened some of those files but could not see any hint. After scanning, I process those files in an identical workflow but somehow some get an embedded thumbnail and others don't. Not a big deal, I was mostly curious than bothered by them. Thank you for clarifying.

Cemal