I tried the one by Canha first, but the placement of the Pin It icon was allover the place, even though I kept choosing the right corner. You also had to edit it in the css section, and it messed up the layout of my gallery pictures.
I tried this one next, and it was so much easier to use! You can make all of your changes in the settings, which is much more convenient. It also has an easy section to choose where you want the icon to be, the opacity level, and you can upload your own image or url. Exactly what I was looking for- I love the level of customization! The only thing that bothers me, is that the pin icon still doesn't show up for images that are in a gallery. Everything else is great though!