SC for 'real' text over a busy background image

I'm working with a client and finding text (real text) that is displayed 
over a busy background image that
obscures its legibility. Currently I don't see a clear SC for this kind 
of problem and it seems to just sit somewhere
under the principle that content must be perceivable. The closest that I 
see is 1.4.5.

Am I missing something?

Thanks

Josh