$ curl -I 
...
content-length: 29297
ignore images that are too large based on http headers content-length
ignore gifs because gif is stale file format
when adding profile pic, make client side compression to eg 500x500 webp
further optimization:
there could be two profile pic files. one small, and one larger when you open profile or click to view full size image
//
you cannot expect any specific behaviour from users. anyone can set any size of profile pic. you can however make clients not to download those.