Is it possible to recognise pain in horses from their facial expressions?

Yes! I study psychology and learned about this ;)
Yes there are ongoing studies about this at the moment actually and specialists are also trying link different facial expressions with particular body discomforts.I'ts really interesting:)
Yes i think so. A horse's body language can tell you a lot about how he's feeling* if you know your horse's behaviour and something seems strange something may be wrong