I use SnagIt Mac to make screen shots. Used in Microsoft Answers forums Because of the way the screenshots are made they tend to blend in to the background. I would like to a black hairline box around the screen shot so the screen shot wouldn't blend in.
I am aware of drawing rectangles and use all the time within a screen shot. However I have one screen shot utility that has been broken with the change to Yosemite in which, if you have a setting checked, automatically adds a hairline outline around the the shape automatically and you can even set the thickness: fine, medium, large.