Ahhmm, that picture "requirement" is rather a "bug", at least a not intended side effect of the removed picture re-sizing. So to find a nice wording is difficult to me. I am not a advertising texter 
Explanation:
In the past our site system had a picture re-sizing to make pictures fit into a 1024x768 frame. This did work in two steps checking.
1st check: Is the picture wider than 1024 pixel. If yes, resize proportionally to 1024 pixel width and skip check 2.
2nd check: Is the picture higher than 768 pixel. If yes, resize proportionally to 768 pixel hight.
The second check and resizing lead to some longish pictures being re-sized smaller than the thumbnail previews, which are resized proportional to 180 pixel width, without hight limit …
at that time, smaller pictures (below 180 pixel width or height) were not re-sized to 180 pixel width or height ... now that happens.
Now there is no more resizing of the picture itself, but there is still a thumbnail with 180 pixel width generated. And that generation isn't optimal, now...
We always ask to upload "Please upload only BIG Pictures in GOOD quality!" with the smallest videos I know being quarter SD resolutions (320x240, respectively 352x288) and for these a 1:1 screen definition copy picture would be expected, which is still bigger than 180x180 ..., which then generates correct proportional thumbnails with 180px width.