g1smd - 6:25 pm on Nov 8, 2012 (gmt 0)
You should make sure that URL requests with NO parameter returns search results for a default size (preferably a large size) and then use this as the canonical URL that all other pages requested with with parameters refer to. Google will prefer that the URL without parameters is the canonical version.
This works in the same way that example.com/product-listing lists all of the products and
example.com/product-listing?perpage=20&page=3 only lists a few of them, but refers to the "all" page as the canonical URL.