A quick overview of how to get something like this. Not a detailed tutorial im afraid
Work at least double the size of your indeed image so you can scale down at the end making it look more detailed. To get the texture start by rendering clouds, then render difference clouds to get a height map for the texture. The image on the right Shows what it should come out like when its rendered with lighting effects
http://www.splashdamage.com/forums/attachment.php?attachmentid=249&stc=1&d=1246403797
To create the edges of the brick. Create a solid white base for the mortar, draw the bricks as mid grey and use an inner glow to soften the edges. Now you have a height map for the brick shape and the texture just combine them. Play with opacity and blend modes till you get a result your happy with. Image bellow shows the brick height map and the result of overlaying them
http://www.splashdamage.com/forums/attachment.php?attachmentid=250&stc=1&d=1246403891
As with all these steps they require more experimentation and playing. I added a bit of noise to the height map to get a result closer to the one you displayed. After you have your height map you have two options. Go the new normal map method and turn your height map into a local map, or the old quake 3 style and use filter->render->lighting effects, use a directional light source and fiddle the settings to get a result appropriate for the material.
http://www.splashdamage.com/forums/attachment.php?attachmentid=251&stc=1&d=1246404727
The result of this is a a grey scale image that should show the luminosity of your intended image. Which for most images (imo) is actually a lot more important than painting a detailed colour map. All you have left to do it play with the levels as your luminosity map will have too much contrast, overlay some colour (can just be a simple solid colour, don’t really need anything fancy). And throw in a few overlay of sandstone images to get a more realistic look.
Overall its a pretty simple process but requires a lot of time getting the exact contrast and blend between the different height map and getting the lighting effect rendering settings right. Quite a quick effort and could put a lot more time into getting a more worn effect around the brick edges.