Remember, requesting permission for copyrighted materials is a last resort, something you only have to do once you've exhausted your other options for including third party materials. That is, if you're unable to locate open access images, and don't feel confident that your inclusion of copyrighted materials constitutes fair use, only then should you request permission for third party copyrighted materials.
We have included ProQuest's sample permission letter below. If you are seeking permission to include copyrighted materials in your thesis, we recommend referring to this document. You can browse the embedded document on this page or download it to your desktop, and may use it as a template when requesting permission to use copyrighted materials.