If you are using Dropbox you should be able to use Dropbox Uploader.
Bearing in mind that I've never used the Dropbox Uploader in such a way before, in theory, using a sub shell the command should end up something like the following:
./dropbox_uploader.sh upload \
$(dd if=/dev/sda7 conv=sync,noerror bs=64K | gzip -c) \
/path2/backups/sda7.img.gz
Caution: I recommend zipping every image since it will minimize space, and therefore network throughput, time, and most importantly money. You may also want to setup a cron job so that only n backups are stored, (remove the n+1 backup each time) so that you don't run out of space too.
WARNING: You should also setup your Dropbox client software to ignore the /path2/backups/
directory otherwise your storage will blow-up O(n²)!!!