I've used Merlin for years and it works great most of the time. Agree with others that it's a great example of something we should all have on the tiny computers in our pockets.

Until this thread I didn't realise it did photo ID! I took a photo of a black redstart last year and at the time was able to identify it via photos uploaded to social media. But I just tried the app and it got it straight away. It also added it as a new 'lifer' because I hadn't previously logged it via audio ID. Cool!