I started by choosing some pictures.
First I opened up the grass picture I showed you the other day.
Then I went to file>place and chose my second picture
I changed the blending mode on this to hard light and turned the opacity down to about 80%. Then again I went to file>place and chose a third picture
This time I changed the blending mode to hue and left the opacity at 100%. I normally just keep scrolling through the different blending modes until I find something that looks good to me. It's not always the same ones but my favorites seem to be either soft light, overlay and multiply. As you can see this time I didn't use any of those but this is what looked the best this time around. You can also use an eraser to erase parts of a picture that may seem a bit too distracting or don't seem to fit well with the look your going for.
The next step was to merge the layers together. Now I could have left it as is but I chose to do one more thing which was to lower the saturation. You can do that by either hitting cntrl+U on your keyboard or by using a hue/saturation adjustment layer. After all this there was nothing left to do but to save the file.
So lets test it out now and see how it looks on a photo.
I opened up this picture then went to file > place and located the texture I had just made. With the new texture as the second layer I changed it's blending mode to soft light and now the above picture looks like this.
And there you have it. Of course you could lower the opacity on the texture layer to give it a more subtle look. It all just depends on what you like. So go ahead and pull out some of those pictures you have that you don't think are good for anything and start playing around with them. You just might be surprised at what amazing textures you can come up with.