I created this flyer using an image that I rendered myself. Can I include it in the main files?
No. Can can check your original image license. You can take permission to original image author. Without owner permission that will affect future legal issues.
You can Check your Assets :
This is my image I’m the owner. I created the head in Zbrush and I rendered with Corona Renderer in 3ds Max. Years ago was no problem uploading flyers using my personal images. I’m not sure there is something change in the rules nowadays.
Yes. Then you can use.