"Photocasting centres around a single undocumented extension element in a namespace that does not need to be declared," stated Mark Pilgrim, a software developer who conducted a number of tests in an effort to document the feature.More info over here.
"IPhoto 6 does not understand the first thing about HTTP, the first thing about XML, or the first thing about RSS.
"It ignores features of HTTP that Netscape 4 supported in 1996, and mis-implements features of XML that Microsoft got right in 1997. It ignores 95 per cent of RSS and Atom and gets most of the remaining five per cent wrong."
Apple's Photocasting breaks RSS standard

Apple's Photocasting feature in the updated iPhoto program brutally violates numerous Internet standards, including RSS, XML and even HTTP.