隨機獲取圖片的api接口

http://lorempixel.com/1600/900

https://unsplash.it/1600/900?random（國內加載略慢）

https://uploadbeta.com/api/pictures/random/?key=BingEverydayWallpaperPicture【返回必應圖片】

https://uploadbeta.com/api/pictures/random/?key=%E6%8E%A8%E5%A5%B3%E9%83%8E【隨機美女圖片】

http://cn.bing.com/HPImageArchive.aspx?format=js&idx=0&n=1（必應返回JSON數據，具體百度