Microsoft windows comes with Snipping tool to capture screen shots with several option and tool like eraser, marker and highlighter. By using this toll one can capture entire desktop, window or some region of windows using rectangular or free form snip. This is good tool for capturing screen on windows.
Adding tags to jpeg images is always better to indexed by Search Engines.
If you are using this tool then you can add date taken meta data in both PNG and JPEG format and you can add tags when you are saving captures to jpeg format. Adding tags are good if you are publishing those captures to internet.