Toggle image source with fade effect

Toggle image source with fade effect


I'm trying to create a cover swap effect for a book. Basically, I want the image source to change from img1.jpg to img2.jpg when I press the "back cover" line. If I press the "back cover" line again, the source changes back to img1.jpg. Also, when the covers are swapping, there will be a fade effect.

I can only do the img1->img2, but not the other way. And I have no clue how to make a fade effect. Can anyone help my please?