Algorithms for named entity recognition
I don't really know about NER, but judging from that example, you could make an algorithm that searched for capital letters in the words or something like that. For that I would recommend regex as the most easy to implement solution if you're thinking small.
Another option is to compare the texts with a database, wich yould match string pre-identified as Tags of interest.
my 5 cents.
I would like to use named entity recognition (NER) to find adequate tags for texts in a database.
I know there is a Wikipedia article about this and lots of other pages describing NER, I would preferably hear something about this topic from you:

What experiences did you make with the various algorithms?
Which algorithm would you recommend?
Which algorithm is the easiest to implement (PHP/Python)?
How to the algorithms work? Is manual training necessary?

Example:
"Last year, I was in London where I saw Barack Obama." => Tags: London, Barack Obama
I hope you can help me. Thank you very much in advance!