Retrieve deleted photos

Check the Recently Deleted album. If you "just" deleted the photos from some other part of Photos – and it has been less than a month since you did the accidental deletion – the photos may be in the Recently Deleted album, from where you can get them back.

See the "Recover deleted photos or videos" section of

Delete photos on your iPhone or iPad - Apple Support

Otherwise, if you don't have backup copies, the photos are gone. (Barring odd cases where you, e.g., sent a photo to your friends or family, and they still have a copy that they could send back to you.)

By restoring them from a backup, created before they were deleted.

No backup = No recovery, sorry.