Photoshop has such mindshare in the work world. Any time people think professional photo editing, they think Photoshop. And it is a great tool. But it is way overkill for what most marcom folks need.
I used the awesome web site AlternativeTo to find Mac alternatives to Photoshop. Pixelmator was high on the list, and for good reason. It has some amazing and easy-to-use photo editing features. Check out the 2-minute video on this page for a pretty fantastic overview of what it can do. The repair tool (a.k.a. healing brush) alone is worth the cost of the app.
I cannot recommend this app highly enough. I am standardizing our who marcom team on it.