Hello guys!I tried to upload my picture for an avatar,which meets the 185x185 qualifications,but it wasn't accepted and was considered invalid.Why is this happening?Is it maybe because it's bmp?

Try uploading it to Imgur, then pasting the direct link in.

Well I had a second look at it and I saw that it was 101 kb which is larger than the requirment:(Is there a way to make it smaller?

save it as a jpg