You'll need some error code, but this works:
JSON={"data":{"id":"TjJuJ29","title":null,"description":null,"datetime":1403695169,"type":"image\/png","animated":false,"width":1538,"height":839,"size":733684,"views":0,"bandwidth":0,"favorite":false,"nsfw":null,"section":null,"deletehash":"lCqsN0tKqWyJFET","link":"http:\/\/i.imgur.com\/TjJuJ29.jpg"},"success":true,"status":200}
Key = "link":"(http:.*)"}
RegexMathAt(JSON, Key, 1)