Original content is always best
Short video from Google that confirms they don’t take into account whether or not you use stock images on your website as opposed to your own original images when they rank your pages.
However, don’t overlook the importance of original content when it comes to your websites users. Stock images can be useful in many circumstances but more and more people are getting use to the same old look and feel of these type of images as they browse the web so if you can include your own images then do so whenever possible. The search engines may not care but your users will thank you for it.