This add-on solve this issue, you can view the full sized image without going to the advertising page first. It is very convenient and time consuming.
The add-on is an experimental one and is compatible with Firefox 3.2 to 3.5. However the extension has small shortcomings.
It only works with images.google.com and not in local search, such as images.google.co.in.
And there is no alternative way to display the related information of the image page (which is sometimes necessary). Install Skip Google Images Advertising from here.