Here's the yimg's response header when requesting one of the files with no
extension:


(Response Status)	HTTP/1.1 200 OK
Cache-Control	max-age=31536001
Connection	keep-alive
Content-Length	17640
Content-Type	image/jpeg
Date	Tue, 13 May 2008 13:58:25 GMT
Expires	Wed, 13 May 2009 13:58:26 GMT
Last-Modified	Tue, 13 May 2008 13:58:24 GMT
P3P	policyref=http://p3p.yahoo.com/w3c/p3p.xml, CP="CAO DSP COR CUR ADM DEV
TAI PSA PSD IVAi IVDi CONi TELo OTPi OUR DELi SAMi OTRi UNRi PUBi IND PHY ONL
UNI PUR FIN COM NAV INT DEM CNT STA POL HEA PRE GOV"