If you're serious about creating graphics, you may want to join me in using Photoshop. I get Photoshop in my Creative Cloud membership, along with Adobe Audition for sound editing, Illustrator and several other Adobe products for $49.99 per month.
Need to learn Photoshop?
Samantha Angel and I teach a complete course for content creators.
The Image Suite plugin lets you edit images right in your WordPress dashboard.
YouZign is a 100% web based graphic design program with a lot of templates to take advantage of.
I also use eCover Authority to do 100% web based graphic design for eCovers and Mock Ups.
Extra Graphic Resources:
My Design Deals – Great source for fonts and graphic elements in huge bundle deals.