Extracting as much information from a browser request as possible?

I am currently working on project that involves identifying spammers which are creating fake accounts on my site. I am interested to know what type of information I would be able to extract.

First of all, there is browser fingerprinting. According to the library http://ift.tt/1AX7o2F, there is about 25 features that I can use.

Then there is platform detection, available at http://ift.tt/1Yh1Mbh. This library seems to be able to extract some information about the uesrs' platforms.

And then I could also extract information from my http server by inspecting the environment.

Are there any other techniques I could use to extract information from my requests?