How do I remove an object, person or watermark from a photo?

For objects and people, the free tool is probably on your phone or PC already: Google Photos' Magic Eraser (brush or circle what to remove, then tap Erase), Clean Up in the iPhone Photos app on iPhone 15 Pro and later with Apple Intelligence, and Generative Erase in the Windows Photos app, which runs on the device so the photo never leaves your computer. All of them invent what was behind the object, so check the edges. A watermark is a different question. If it is a stock agency's or a photographer's mark, it is not yours to remove: license the picture instead, and note that in the US removing copyright management information to hide infringement is itself unlawful under 17 U.S.C. 1202. If it is the mark on an image Gemini made for you, removing the visible mark does not remove Google's invisible SynthID watermark, which is built to survive cropping and filters and which Gemini's checker reads. Rule: erase clutter freely, and license rather than clean other people's pictures.