I suppose one of the most comprehensive keys is the Delta IntKey system but I didn't find it user friendly (actually that is an under statement) and it doesn't even auto load. You have to enter the programme into your computer through 'the back door' like so many other complicated programmes that were available a few years ago.
And after your free month's trial it definitely isn't cheap. Around £300 if I remember correctly!
But there are a few freebies associated with the main programmes. So if anybody wants to have a look here is the main starter page
DELTA System - Overview but where you go from there is anybody's guess.
Incidentally, I did manage to install it once but didn't pay to continue.
Anyhow, back to reality. Be careful about internet identification as many sites are US based but that isn't always clear at the start; although they may still work well to get you to basic family level.
The Aidgap booklets are reasonably priced and I find them easy to use. Well most of the time anyway!
But any ID keys can be a struggle to use with photos, as I'm sure you are already aware. Too often, I find myself shouting at the book 'I can't see that can I' when one simple difference makes a choice between several totally different families. Often I do better by starting with an illustration and working backwards from that.