When ever you enter a new forum or subforum you should make it good practice to always check for stickied threads at the top.
If you had you would have found this:
http://www.automotiveforums.com/vbul...d.php?t=294063
For your needs you will have trouble with a free site, I doubt you will find the space you need.
However most of the sites listed in the stickie thread at the top have payed member options which give you much more space.
Pbase is regarded as one of the best professional sites out there while something like photobucket is aimed more at the amature. And of course thier prices and features reflect that.
And remember that its useless trying to post an image larger than 1024x768 on the internet as most people will not be able to view the whole image at once, and if your posting in a forum anything larger than 800x500 will not fit with in a post and people will also not be able to view it.