You can use a greyscale version of the image texture to create either:
- a Bump Map or
- Mesh Displacement via the Displacement Modifier.
The Bump solution is the lighter, less resource-intensive solution, and it will be easier to render. However it will give you the illusion of craters on the surface, and will not affect the silhouette of the object.
The Displacement modifier solution will give you actual changes to the surface of the mesh and WILL affect the sillhouette of the object. However you will have to subdivide the mesh (or apply a SubDiv modifier) many times to get a good clean result, and this will make the mesh difficult to work with. Another challenge of this technique is that it works better with higher bit depth images. Higher bit images (16bit, 32bit) have a wider variance between dark and light values, giving more variance in the range of the displacement effect. For most scenarios, however, you'll likely be working with 8bit images which doesn't provide a huge range in displacement values.
In reality, you'll probably always want to set up the Bump Map. It will give the fine details you need. The Displacement mod is really only helpful for larger features on the profile of mesh. You can always use both together if need be.
Here's a screenshot with an asteroid with Bump Map only (on Left).
Here's a screenshot with the asteroid with Displacement only (on Right)