Are you trying to post a picture?
Best suggestion is to right click -> save as, then upload to a free image hosting such as
www.imageshack.us or
www.waffleimages.com .
Photobucket.com is good as well, except it has account requirement, however you can save the image for future use.
Then simply click the image icon and enter address the site gives you.
If you find a picture you want to post on a random site, well, alot of random sites if you just enter the address the site hosting has hotlinking blocked so nobody can view the image unless you've been to the site. This results in a red x for the forum users, even though you can view the image just fine (because you've visited it, and it's stored in your cookies).
Pffft. And mods think I'm useless.