There are a lot of ways to do this.
Open up the desired image. Duplicate the image.
Then in a new layer type something (make sure the font size is as big as you want it (really depends on the image. You can decrease the opacity and move the text around so that you find the way you prefer the image to line up. Then use the Magic Wand to select every letter of the text.
Once selected you can hid that layer. Go to the duplicate photo layer and then hit select inverse and then hit delete. Then crop the text however you like.
You can then delete the original photo layer and the text layer.
Save it as a PNG so the background is invisible.