To add a sticker to a photo on an iPhone, follow these steps:
- Open the Photos app and select the photo you want to add a sticker to.
- Tap the Edit button.
- Tap the Markup tool, represented by a pen icon.
- In Markup, tap the + (plus) icon and select "Add Sticker" from the menu.
- Choose a sticker from the default Apple stickers or your custom sticker library.
- Drag, resize, rotate, and position the sticker as you like on the photo.
- Tap Done to save your edited photo.
Additionally, you can create custom stickers from your own photos by long- pressing on a photo subject in the Photos app and selecting "Add Sticker" to add it to your sticker library for use in Markup or Messages.