The main benefit you get from using our online image markup tools is that the markup can be edited again later whenever you want, and as many times as you want, without ever leaving Dozuki or affecting the quality of the original image. We layer our Image Markup on top of your pictures, leaving the original image in tact.
While Snagit does look like a pretty useful desktop screen capturing tool, it's unlikely that we'll be developing a Dozuki plugin for it in the near future, as that would take quite some time to develop.
We have plans to improve Dozuki's image markup by adding another highly requested type of markup for you to use: a colored arrow. Using arrows on your images will make it easier for you to correctly convey motion in your pictures, without needing to use multiple pictures one after another. Do arrows in markup seem like they would a useful tool for you to use?