Instead of making a grass texture out of a photo I thought it would be better to just create my own and bake it down.
I used Twist, Bend and FFD modifiers to change shape of individual blades.
I rendered them as a 2048 x 2048 sheet and the only thing left was to change the hue of each bunch to give it a bit of variety. The good thing about this technique is that you instantly, together with diffuse render, get an alpha image. Therefore I didn't have to waste time to mask it out manually in Photoshop.
There is so much space left in this texture sheet; I will probably add some weeds later on.
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