Dropbox has pretty harsh bandwidth limits for files that are hosted publicly, mainly to avoid becoming a cheap & lazy webserver for everyone to use. They additionally have the difficulty that the photo could change at any moment -- so photo URLs from their CDN have all this complicated versioning:

https://photos-1.dropbox.com/pi/2048x1536/UoBdS4hHgypeXF5Ge8...

I guess my point is that it would be great, but you can have imgur or Dropbox -- not both.