func createGIF(with images: [UIImage], loopCount: Int = 0, frameDelay: Double, callback: (data: NSData?, error: NSError?) -> ()) {
    let fileProperties = [kCGImagePropertyGIFDictionary as String: [kCGImagePropertyGIFLoopCount as String: loopCount]]
    let frameProperties = [kCGImagePropertyGIFDictionary as String: [kCGImagePropertyGIFDelayTime as String: frameDelay]]
    
    let documentsDirectory = NSTemporaryDirectory()
    let url = NSURL(fileURLWithPath: documentsDirectory)?.URLByAppendingPathComponent("animated.gif")
    
    if let url = url {
        let destination = CGImageDestinationCreateWithURL(url, kUTTypeGIF, UInt(images.count), nil)
        CGImageDestinationSetProperties(destination, fileProperties)
        
        for i in 0..<images.count {
            CGImageDestinationAddImage(destination, images[i].CGImage, frameProperties)
        }
        
        if CGImageDestinationFinalize(destination) {
            callback(data: NSData(contentsOfURL: url), error: nil)
        } else {
            callback(data: nil, error: NSError())
        }
    } else  {
        callback(data: nil, error: NSError())
    }
}