WP Retina 2x creates the image files required by Retina and displays them to your visitors accordingly. Check the official page about the plugin here: WP Retina 2x.
The Yearly Standard license is recommended. This license will always work as long as it is active. The lifetime license is, of course, active forever.
If you don’t like it, or it doesn’t work for you, no worries. I will refund you immediately. Please contact me within 3 weeks in this case.