A deleted photo is not always gone. Try these steps in order, and start as soon as possible: new photos and downloads can overwrite the space of deleted files.

1. Check the trash first

Gallery app: most phones keep deleted photos for 30 days in "Recently deleted" or "Trash".
Google Photos: open Library › Trash. Backed-up photos stay there for 60 days.
Cloud apps: OneDrive, Dropbox or your phone brand’s cloud may have a copy.

2. Scan the phone with a recovery app

If the trash is empty, a recovery app can search the storage for files and thumbnails that are left behind. With Deeps Recovery:

Allow All files access. It enables the deepest scan, including hidden folders, caches and the SD card.
Choose Photos. Each file type has its own scan.
Start with a quick scan; if your photo is not found, run a deeper scan (see Quick, Deep or Full Scan).
Preview the results, filter by folder, date or size, select your photos and restore them.

Restored photos are saved in their own folder so nothing is overwritten. See Where Are Recovered Files Saved?

No app can guarantee that every deleted file comes back. Often only a smaller thumbnail survives. Results may also include photos that still exist on your phone.

3. Avoid losing photos again

Turn on Google Photos backup.
Hide private photos in the Private Vault instead of deleting them.