API request of form http://en.wikipedia.org/w/api.php?format=json&action=query&generator=search&gsrsearch=Samuel%20Paley%20Park%20New%20York&gsrnamespace=6&gsrlimit=50&prop=imageinfo&iiprop=url%7Cdimensions%7Csize%7Ccanonicaltitle%7Ctimestamp%7Cextmetadata&iiurlheight=200&iiextmetadatafilter=License%7CLicenseShortName%7CLicenseUrl%7CArtist%7CImageDescription%7CGPSLatitude%7CGPSLongitude returns 503, Service Unavailable although changin the query string in gsrsearch by only one letter fixes it - adding or deleting any character to Samuel%20Paley%20Park%20New%20York works.
Removing prop=imageinfo seems to work as well.