from the photo's aplication on your ipad there should be a export button [looks somewhat like a box with an arrow coming out of it] and there should be an option for e-mail and a few other things. you need the facebook app installed on your ipad for this, dont worry though its free but once you have installed it there should be a facebook option under the export menu click that and it should come up asking for user name password ect.
from any I device or even android the steps should be the same or similar
EDIT: just realised you ment for the site.
http://imageshack.us/content.php?page=iphone is an app for the iphone that will upload to image shack from which you can hotlink images.
most other photo sites should have an app i assume [i use image shack and find it works fine]