Is it possible to create a gallery with very simple image gallery, where enlarged image differs from thumbnail?

Q: I'm making a cake shop's gallery page for my client.

Can I have the thumbnail showing a photo of a cake, and after click to enlarge, it shows another photo (which is a photoshopped photo with the cake on the left, and the cut-in-half cake on the right)?

A: VisualLightBox generates thumbnail using original image. It's impossible to change it.

You can try to create 2 separate galleries (1 - for thumbnail, 2 - for main images) and then combine them (exchange thumbnails of the 2 gallery on thumbnails of the 1 gallery).