If you view that same folder, then choose to turn icon previews off (the icons should all show the generic icon), then turn previews back on, do the exact same file icons remain with generic icons?
I also notice that your folder is named "Shared folder"...
Do the generic files belong only to your (or only to someone else who shares the folder)
Of course, I also notice that the filenames seem to be in sequence, so those would, in any case, be from one source (?)
Are there a LOT of pictures in that folder (a lot is for this purpose, more that several hundred)?
In that case, you may simply not allow the system long enough to "interpret" all of the previews.
I wonder if it would be worthwhile to reset your spotlight database, allow it some time to rebuild, then look at your folders again.
You might also try resetting the Launch Services database.
There's some other possible fixes
here ...