imgformat.swift

import MobileCoreServices

extension String {
  func isImageExtension(_ ext: String) -> Bool {
    let uti = UTTypeCreatePreferredIdentifierForTag(kUTTagClassFilenameExtension, ext, nil)
    guard let imageUTI = uti?.takeRetainedValue() else { return false }
    return UTTypeConformsTo(imageUTI, kUTTypeImage)
  }
  
  func isImageLink() -> Bool {
    let ext = (self as NSString).pathExtension
    return isImageExtension(ext)
  }
}

"http://www.my-image.com/1.jpg".isImageLink()     // true
"http://www.my-image.com/2.jpeg".isImageLink()    // true
"http://www.my-image.com/3.png".isImageLink()     // true
"http://www.my-image.com/4.tff".isImageLink()     // true