random_image.R

random_image <- function() {
 ## Return the URL random image in Wikimedia Commons
 random_query <- paste0("https://commons.wikimedia.org/w/api.php?",
                        "action=query",
                        "&generator=random", # get a random page
                        "&grnlimit=1",       # return 1 page
                        "&grnnamespace=6",   # category: File
                        "&prop=imageinfo",
                        "&iiprop=url|size|extmetadata",
                        "&iiurlheight=1080",  # limit images height (sometimes)
                        "&format=json&formatversion=2")
 random_response <- POST(random_query)
 output <- content(random_response)
 url <- output$query$pages[[1]]$imageinfo[[1]]$url
 ext <- tolower(file_ext(url))
 w <- output$query$pages[[1]]$imageinfo[[1]]$width
 h <- output$query$pages[[1]]$imageinfo[[1]]$height
 size <- output$query$pages[[1]]$imageinfo[[1]]$size
 desc <- output$query$pages[[1]]$imageinfo[[1]]$extmetadata$ImageDescription$value 
 if(w<50 || h<50) stop("Image too small") 
 if(size > 4000000) stop("Image too large")
 if(!(ext %in% c("jpg","jpeg","png","gif","bmp"))) stop(paste("invalid image type:",ext))
 attr(url, "dims") <- c(w=w,h=h)
 attr(url, "desc") <- desc
 url
}