Mouse-over for Larger Photo

Hi,

Just posted another question, but I think it’s most helpful for future search requests with each question in a separate thread.

I’m browsing at https://www.themeforest.net and when you mouse over any thumbnail the photo pops up large and as soon as the mouse is off the thumbnail the image disappears.

How is this possible? Coolest effect ever!! I’d love to have that on my daughters website for her album.

Thanks,
Bryce