Since I found this post just now trying to figure out why my avatar image was "wrong image type" I did this:

1. As stated above right-click and select the image link option.
2. Paste into the avatar URL field on your profile, but (in the case of Safari and Imgur):
a. Make sure to trim off everything after the file extension in the filename.
b. Change the extension to .jpg

In my case I pasted in: https://i.imgur.com/iYbgOFj_d.jpeg?maxwidth=520&shape=thumb&fidelity=high

I had to trim off everything after ".jpeg", and change it to ".jpg". Only then would my avatar URL save correctly.

Just your average urban druid interested in the great outdoors and quantum cosmology. 

(Pronounced: Dru-nehm-ah-tän)