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<?php $json='{"http://ecx.images-amazon.com/images/I/51Lg%2Bd4cqRL._SX355_.jpg":[355,266],"http://ecx.images-amazon.com/images/I/51Lg%2Bd4cqRL._SX425_.jpg":[425,319],"http://ecx.images-amazon.com/images/I/51Lg%2Bd4cqRL._SX466_.jpg":[466,350],"http://ecx.images-amazon.com/images/I/51Lg%2Bd4cqRL._SX450_.jpg":[450,338],"http://ecx.images-amazon.com/images/I/51Lg%2Bd4cqRL.jpg":[500,375]}'; echo(implode("\n", array_keys(json_decode($json, TRUE))));