You could add a "Download this page" button on the page which does some tricks to produce an HTML file with the images baked in that the user can download, which could work on mobile.

Here's a quick prototype: https://gistpreview.github.io/?14a2c3ef508839f26377707dbf5dd... - code here: https://gist.github.com/simonw/14a2c3ef508839f26377707dbf5dd...