We generally encourage you to use only the photos available in our submission kit for each challenge. If you are looking for a type of photo that we have not included (for example a photo of a pet, etc.), please email us at firstname.lastname@example.org to ask if we can add photos to our submission kit.
That said, if you have a specific type of photo that we can't provide, you may use one of your personal photos for submission. Keep in mind that these images are placeholders for the purposes of submission and will not be permanently attached to your design.