There is probably something unusual with that picture, but I don't know enough about image files to pinpoint why it won't display in Winamp.
I'm pretty sure it's not because of its size.
I can display another folder.jpg that is 74 MB (25,700 x 20,400): 82 MB causes my Winamp to crash. (I had Auto Restart enabled, so that was exciting for a minute!)
I guess the maximum size is somewhere in between.
It displayed OK in any image viewer I tried.
ImageMagick can resize it, but
Photo Resizer can't.
There are all sorts of image processors: I suspect the good ones will handle it and the weaker ones won't.
It is displayed oddly in Mp3tag when embedded in a MP3 or FLAC and will not display in Winamp.
If most of its metadata is stripped, it displays normally in Mp3tag but still won't display in Winamp, either embedded or not.
Seems like another rare, oddball case that Winamp is not robust enough to handle.
It's easy to fix by opening it with Paint and saving it as a JPG.