Change header_background based on UserGroup

[stl7997]

Pretty much what the title says. Is there a way to have two different header_background images for unregistered and registered usergroups?

I would like to customize a header in photoshop to say 'Welcome to ..... " and have a pencil brushed arrow pointing to the register link (fixed layout).

However I don't want that image to appear for my registered users after they log in.

Any way to do this?

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After thinking about this, I don't think it would work due to browser cache.

[princesspepper]

I would like to do something similar, but have the trigger as date, rather than usergroup, so that I can make special date images for valentines day or Easter and have the headers automatically change on those dates. Any ideas?