The background photos in the new dashboard change daily so you don't have to worry about the fly. If you don't like it today, it'll be gone tomorrow.

However there is a new add-on (still pending approval) to allow you to do just that. Find it here- http://www.concrete5.org/marketplace/addons/dashboard-images/...

I rather enjoyed being startled this morning by an enormous bug... Opps.. Must be the wine talking tonight!