Make sure the case (lower / upper) are the same and link the entire path of the location of the gif, not just the folder.
In other words:
Code:
<img src="http://www.example.com/images/picture.gif">
as opposed to:
Code:
<img src="/images/picture.gif">
Wordpress can be a little fussy when it comes to images especially when you're using templates. It seems to work when you put the fuill path to the picture in the tag and not just the folder/file