The rest of this book is mostly about *making* images — better, brighter, sharper, or out of nothing. This part is about *believing* them. Cheap editing tools, and now generative models that synthesize a convincing photograph from a sentence, have severed the old reflexive link between "photograph" and "something that happened." Two responses run in parallel. **Forensics** works on an image you are handed cold — no cooperation, possibly an adversary on the other side — and looks for the statistical and physical fingerprints that authentic capture leaves and editing or generation disturbs. **Authentication** works the other way around: it asks creators and cameras to *sign* their work and every edit to it, so trust comes from a verifiable record rather than a hunt for tells. Neither is sufficient alone — forensics gives evidence, not proof, and provenance is opt-in — so the honest position is that they are complementary.