Skitch is an app that I use all the time both in my personal meandering a through life as well as in the work I do as a teacher. The problem is that Skitch has been discontinued by Evernote.
This by Tinrocket ($1.99) is a new alternative I’ve discovered tonight. It is an app made to do one thing and do it simply and easily. This allows you to ad pointers, labels, descriptions and commentary to your pictures.