Tease and tantalize your fans so they can't resist clicking on your photos.
Do it by zooming in on the most interesting part of your photo. When they click on the thumbnail, they'll see the rest of the picture.
The Easiest Way
On the Customize Gallery page, you'll see a Square Thumbs option. Toggle that to yes, and all photos in that gallery will automagically get a zoomed in, square thumbnail.
A bit more picky?
To choose exactly what part of your photo will be in the thumbnail, make sure you're logged in. Select Zoom Thumbnail from the Photo Tools Menu. Here's what you'll see:
You can ignore everything on the left and just click the blue square you see on the lower right of the photo. Hold your mouse down and drag to resize the zoom area. Click near the center of the larger box and drag to move the zoom area around.
Click save changes. That's all there is to it.