By default all deleted photos/videos go to "recycling bin" for 30 days and then get completely deleted. But one can go there and completely delete it earlier. After that it's most likely impossible to recover it. There's also a chance it might've been uploaded to cloud but deleted only on the device.
iOS has had storage encryption enabled by default since the iPhone 3GS (2009) so you’re not going to be able to recover anything from the hardware and applications have to work at it to retain data unintentionally. This is bad for data recovery and forensics but makes it much safer to sell a device.