A link to a fullsize .jpg certainly passes pagerank to that image. In fact, that is one of the absolute best ways to get images to rank in image search. Instead of putting the large image in the page with a img tag, use a thumbnail in the page and link to the larger version. This works because 1) Google passes pagerank to the image when it is a link but 2) Still considers the image to be part of the page and 3) bigger images just rank better and you can link to really huge ones if you want.
On the other hand, I really doubt that this hurts your site. Google did a lot of work a few years ago to redistribute lost pagerank from your site back to your important pages. There are lots of links that just drop pagerank on the floor: 1) nofollowed links 2) Links to pages in robots.txt 3) Links to images
When I have removed these types of links from my sites, it makes no difference.