Ideas for how to give focus to an element

Hey, i’m making a landing page, and it has a gallery in it. I decided to make it a little different, i have thumbnail for each image in the gallery and whenever you hover over the thumbnail, the full screen image changes.

The problem is, it’s a bit hard to see it, it’s not difficult to see per se, anyone can in fact see the thumbnails, but it’s not…polished, i guess. Any ideas on how to make it more noticeable? Everything i tried looked worse than picture below.

How about giving the thumbnails a thick white border (say, 3 to 5 px thick, I don’t know)? Then try throwing in a black box shadow.