Adding a contrast checker for background images

[bdeclerc]

One thing that's lacking (here and in other tools I've seen) is the ability to verify contrast between foreground text and a background image - right now the tool simply alerts on the potential issue, but it would be awesome to find a way to do an actual contrast check.

Of course that's more complex than with plain colour, but it's not unimaginable.

I've found a tool that actually does something like this - https://github.com/kennethcachia/Background-Check - as a future enhancement we could investigate if it's possible to integrate such a check in some way.

[bdeclerc]

This will (attempt to) be handled through an innovation project using AI tools, the intention is to integrate those solutions back into the tool during that project.