I was in Wikipedia today and and got a cookie request (from Firefox) for s.ytimg.com - of course I blocked it, third party cookies for cryptic domains are usually questionable. But the fact that it turned up while I was in Wikipedia made me wonder what it was.

So I looked into it...  then I unblocked it.

 

For those that don't know, I always surf with all cookie warnings turned on - mainly because I object to many - but not all - third party cookies on principle. Sure... show me advertising if you must - but I choose not to reveal my browsing habits to you.

So, what is s.ytimg.com?

$ whois ytimg.com

Registrant:

        Google Inc. (DOM-1723647)

        1600 Amphitheatre Parkway

        Mountain View CA 94043

        US

    Domain Name: ytimg.com

        Registrar Name: Markmonitor.com

        Registrar Whois: whois.markmonitor.com

        Registrar Homepage: http://www.markmonitor.com

    Administrative Contact:

        DNS Admin (NIC-14290822)  Google Inc.

        1600 Amphitheatre Parkway

        Mountain View CA 94043

        US

        dns-admin@google.com

        +1.6506234000

        Fax- +1.6506188571

    Technical Contact, Zone Contact:

        DNS Admin (NIC-14290820)  Google Inc.

        1600 Amphitheatre Parkway

        Mountain View CA 94043

        US

        dns-admin@google.com

        +1.6506234000

        Fax- +1.6506188571

    Created on..............: 2007-Dec-11.

    Expires on..............: 2008-Dec-11.

    Record last updated on..: 2007-Dec-11 14:40:32.

    Domain servers in listed order:

    DNS1.SJL.YOUTUBE.COM

    DNS2.SJL.YOUTUBE.COM

 

Oh! It's a you tube domain!

$ nslookup s.ytimg.com

Non-authoritative answer:

s.ytimg.com          canonical name = static.cache.l.google.com.

Name:                  static.cache.l.google.com

Address:              74.125.4.21

 

Yep, it really is, it's even got a canonical name in Google. Hmm... the name implies a cache, and the ‘yt' in ‘ytimg.com' is probably for You Tube, and if so the ‘img' probably stands for image.

A You Tube image cache? So it would seem. 

A quick google URL search turns up lots of image tags that include it, I also found a couple of discussions:

• Read i.ytimg.com
• What would you call this protocol for displaying images?

 

Given that these references within the ytimg domain are probably being generated on the fly, I suspect that the code behind them is probably doing something with the cookies (including the obvious tracking).

So I have decided to unblock the whole ytimg.com domain, although in my case I have set the domain to "Allow for Session" in Firefox.