pageoneresults - 1:17 pm on Mar 9, 2011 (gmt 0)
Use this as a reference for the alt attribute in HTML5...
HTML5: Techniques for providing useful text alternatives
The longdesc has been deprecated in HTML5. There are plenty of folks who are not happy with that decision.
If it were me, I surely WOULDN'T be taking the HTML5 advice and stuffing an alt attribute with an entire description like they show as examples. Remember, the text alternative takes up visual display space and may interfere with surrounding text.
I'd look at all the other methods available before putting more than 80 characters in the alt attribute. The W3 have recommended 80 characters as a suggested limit when composing a short text alternative.
In regards to the topic, don't let them hotlink! If you rely on image search for revenue, then you should plan on blocking all but those that you will allow to hotlink. Don't ask me how to do this either, talk to your dev. Let them know that you need to allow Google and maybe a handful of others to hotlink. All the rest get a 403 and/or a special message just for hotlinking swine! ;)
Are Image Theft and Hotlinks Creating an Algo Disaster?
In my personal opinion, yes they are. There are patents from Google that discuss hotlinking and how they may use it in their algo. Hotlinking can be good in some instances and in this instance (topic at hand), it can be bad.