My fiance just asked if it was possible to increase the size of the thumbnails (96x96 pixel default) in her windows dialogs. Luckily, I knew this was one of the many options that can be tweaked by using the TweakUI Windows PowerToy which is a free download from Microsoft.

Once you download and install TweakUI, click Explorer then Thumbnails in the treeview.

Try different thumbnail pixel sizes until you are satisfied.