Upload image with multipart form-data iOS in Swift

i am having a problem with uploading image with multipart-form

here is my code i used from this answer

    var request = NSMutableURLRequest(URL: url!)
    request.HTTPMethod = "POST"


    var boundary = generateBoundaryString()
    request.setValue("multipart/form-data; boundary=\(boundary)", forHTTPHeaderField: "Content-Type")

    var body = NSMutableData()

    if self.img.image != nil {
        var imageData = UIImagePNGRepresentation(self.img.image)

        if imageData != nil {
            body.appendString("--\(boundary)\r\n")

            body.appendString("Content-Disposition: form-data; name=\"image\"; filename=\"image.png\"\r\n")
            body.appendString("Content-Type: image/png\r\n\r\n")
            body.appendData(imageData!)
            body.appendString("\r\n")
        }

    }

    body.appendString("--\(boundary)--\r\n")
    request.setValue("\(body.length)", forHTTPHeaderField:"Content-Length")

    request.HTTPBody = body

then i use NSURLSession to apply the request

the server says that i didn't choose image to upload i only want to upload the image for now

do i have to use paths of images to upload any image or it's data is enough?

do i miss any thing , any help to understand this ?