If you are getting back this error, "Input data for tag Item.PictureDetails.PictureURL is invalid or missing. Please check API documentation.", it could be because you are using in invalid URL.
The issue is that the underscore character is not a valid character for a domain name, please see http://en.wikipedia.org/wiki/Domain_name. “The Internet standards (Request for Comments) for protocols mandate that component hostname labels may contain only the ASCII letters 'a' through 'z' (in a case-insensitive manner), the digits '0' through '9', and the hyphen ('-')” So our framework failed to de-serialize.