Check if string name matches an asset in images.xcassets

Just a bit more practical answer: Swift

if let myImage = UIImage(named: "assetName") {
  // use your image (myImage), it exists!
}

This is one way to check it.

NSString *someString = @"SomeStringFromSomwhere";

 if ([UIImage imageNamed: someString])
 { 
    //the image exists..
 } 
 else
 {
    //no image with that name
 }