Image use is a bit more complicated than that. You basically have to have permission to use the image. In order to check if you have permission, it's good to cite the image source. Additionally, it's a requirement of some licenses. But you also have to check the license to see if you really can use the image, and if you need to do anything in regards to how you use it.
The Shutterstock image you used, is not licensed, and even if you had licensed it, you would have had to include the copyright under it.
Thanks for the input here @geekpowered! If you have a second, check out @glenalbrethsen's comments above to see if they go along with what you're saying. Thanks again :)