Board Thread:Support Requests - Getting Technical/@comment-12198205-20140530122129/@comment-856287-20140531003515

You can use the template to define the default (non-hover) image and that can change for each instance you use the template, but a wiki template won't be able to define the new image that appears on hover; that would always have to be the same image for every instance of the template.

...at least, if you're going to use CSS to do it. The :hover selector is a "pseudo class" and so you can't define that in an inline style like a template uses; it would have to appear in the (which you can't really edit on Wikia) or an attached stylesheet (like Special:CSS.

If you only have a few different images that should show up on hover, you can define each one in Special:CSS and then use specific classes in the template. However, if this is supposed to be fully dynamic (anyone can define any image, and then any hover image as well) you'll have to use javascript instead.