Missive skin supports replacing one image with another, https://jalbum.net/en/skins/skin/Missive

Sample albums and user manual at https://robm.jalbum.net/Missive%20for%20jAlbum/

Sample of alternative image in slide page mode, click on the triangle of three arrows to show the other image, with its own title and comment.
https://robm.jalbum.net/Missive%20slide%20pages/Architecture/slides/zq-lee.html

There is also a mode where all images are on a single page.

On missive skin settings, under images enter a name for a folder to hold the alternative images.
Next, in any part of the project you want to have an alternative image add a subfolder of that name, then add images using the same file name as the 'normal' image.

Sample slide mode project so you can see how it is structured and works
https://robm.jalbum.net/Missive%20slide%20pages/jAlbum%20project/index.html