IRCC does ask for relationship evidence, and the official spouse checklist specifically mentions wedding, engagement, celebration and outing photos as possible proof. It allows up to 20 photos from different times and places, with a brief description of each.
I could not find any official IRCC guidance saying that digitally altering relationship photos for religious reasons is acceptable. Because the purpose of the photos is to show that the relationship is genuine, I would avoid edits that change your appearance or the context of the image.
If sharing certain photos conflicts with your religious beliefs, IRCC’s guidance allows applicants who cannot provide a requested item to include a detailed written explanation and other supporting evidence. You can strengthen the application with proof of contact, visits, shared finances, joint documents, or letters from family and friends.
So I would submit only photos you are comfortable sharing in their original form, explain the religious concern in writing, and provide strong alternative evidence rather than modifying the photos.