how to identify whether a person is online or not

I am creating a userprofile type of thing in my site i want to show all user SKYPE status whet开发者_如何学运维her online or offline how to do

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If you just want to show their status you could add the following link the their real skype status with:

<img src="http://mystatus.skype.com/smallclassic/USER-SKYPE-NAME-GOES-HERE" />