PicMonkey.com has been a total game-changer for me when it comes to creating eye-catching workout images. It’s incredibly user friendly and FREE, unless you want to pay $5 a month for a upgraded version, which I personally think is more than worth it. (The upgraded version gives you access to a lot more fonts, editing effects, images, etc.)
Playing around with PicMonkey is the best way to familiarize yourself with the site and get comfortable creating and editing images. Though I usually use Picasa to edit my photos (<