what follows after clustering
If you have ground-truth cluster labels, you can measure Jacquad-Index or something in that line to get an error score. Then, you can tweak your distance measure or parameters etc. to minimize the error score. 
You can also do some clustering in order to group your data as the divide step in divide-and-conquer algorithms/applications.
I am trying to cluster images based on their similarities with SIFT and Affinity Propagation, I did the clustering but I just don't want to visualize the results. How can I test with a random image from the obtained labels? Or maybe there's more to it?
Other than data visualization, I just don't know what follows after clustering. How do I verify the 'clustering'