Follow the related link below to add the band to your Twitter picture.
It used to be done by artists, who would make sketches and overlay transparent paper with additions of wrinkles and thinning of facial features. Now, software has been created that will do the same...
Well, it is different for every style, but most bands have a guitar/vocal, bass, and drums. Some have a keyboard.
Pictures can be found all over the internet. Simply search on any search engine. Wikipedia has many photos as well.