First up, if you have an infographic, the smart money is to control how people link to it in some way. Usually, this involves providing them with some kind of embed or linking code. Secondly, if you are a using some SEO smarts here you are going to want them to link to a page rather than to the image itself so you can pump some of that inbound link juice out to other pages or at least control it and provide a little more info, branding, funnels to service pages / social sign ups etc.
So, the way this tends to work is through hosting the infographic on a page and then providing link code to that page something like:
< href="http://www.yoursite.co.uk/">Your Home Page
You may also include a link to your homepage in this to really pimp our link opportunity.
Now, the only problem here is that we are creating a signature for the links as each link is going to be exactly the same. So, this is almost the sitewide scenario where they can count one, but identify and easily discount the others.
But, the real bones of the question is not 'how can Google devalue infographic links' but rather how can we stop Google devaluing infographic links.
Certainly though, an infographic is a high quality piece of content and if people choose to link to it, that link should still count. Whilst, they may look at ways of devaluing these links if they get too widespread but really, the boom (and bust) in infographic production may well have devalued them already in that there are just so many to choose from.
Hope that helps
Marcus