No concerns with Linux, there's an incalculable number of software of display, publishing and retouch. For those who'd like to make of the morphing it's the similar. And supreme favor all these software are free and updated regularly by a team of passionate persons.

It's impossible to quote them all, but the most known by linux users is certainly the gimp, this software is a "free copy" of photoshop quite a lot of functions of which it resumes and the accustomed of photoshop ( Mac) won't be confused, the interface is very resembling.
This product isn't exempt from small bugs, but the participants to the project " the gimp " work to eliminate them. (I know quite a lot of software sold to the price of the gold which also contain bugs) please, don't forget that it's free and updated trés réguliérement.
The gimp is with any distribution (mandrake, redhat, suse etc.) or on Web at the gimp.org address or still on rpmfind.net

Please, also know that quite a lot of " small graphic software " are delivered with distribution in particular with the graphic interface kde.
let's quote loose kpaint, kview.

For the persons who want to make of the vectoriel there's also Adobe Illustrator's "free copy" which is called to killustrator, it is free also.

In conclusion no concerns of the highly-rated of the compatibility of Linux with the world of the digital photo.