I am looking for a driver for Canon SELPHY CP800 under OS X 10.10

Unfortunately, the Canon support website indicates that there are no Yosemite drivers available for the CP800.

You might want to contact Canon Support directly to see if they plan to offer Yosemite drivers for this product.

You might be able to find a driver here.

Gimp - Print

HPIJS for Mac OS X

Hi there

There is a solution, check out the following post:

How to install Canon Selphy 900 on OS X 10.10 Yosemite

Also works for CP800.

Cheers,

Lukas