I have to admit I really liked this idea when I first saw it at plugy pixel working with Photoshop, so I tried it with Pixelmator and it works almost the same way! (Ps. I will look for other good editing programs for PC for you)But well, here is how you can add gradients to your photos!
1. First just open you picture on Pixelmator, 2. Add a layer above your background, 3. Choose a gradient combination or make yours and place it on the new layer, 4. Change the opacity of the gradient layer until you get the look you desire, 5. Add some of your style and have fun!! Adding phrases to pictures always make them have a personal touch (;