Save UIImage array in NSUserDefaults

First of all that is not ideal way to save image in user default but if you want you can do following things

Save

let imageData = NSKeyedArchiver.archivedData(withRootObject: placesArray)
UserDefaults.standard.set(imageData, forKey: "images")

Retrieve

       let imageData = UserDefaults.standard.object(forKey: "images") as? NSData

        if let imageData = imageData {
            let imageArray = NSKeyedUnarchiver.unarchiveObject(with: imageData as Data) as? [UIImage]!
            print(placesArray)
        }

Note: You should save your image in document directory and then save that name array to user default.

Save image in document directory

func saveImageDocumentDirectory(){
        let fileManager = NSFileManager.defaultManager()
        let paths = (NSSearchPathForDirectoriesInDomains(.DocumentDirectory, .UserDomainMask, true)[0] as NSString).stringByAppendingPathComponent("apple.jpg")
        let image = UIImage(named: "apple.jpg")
        print(paths)
        let imageData = UIImageJPEGRepresentation(image!, 0.5)
        fileManager.createFileAtPath(paths as String, contents: imageData, attributes: nil)
    }

Retrieve image

func getImage(name : String){
        let fileManager = NSFileManager.defaultManager()
        let imagePAth = (self.getDirectoryPath() as NSString).stringByAppendingPathComponent(name)
        if fileManager.fileExistsAtPath(imagePAth){
            self.imageView.image = UIImage(contentsOfFile: imagePAth)
        }else{
            print("No Image")
        }
    }

func getDirectoryPath() -> String {
    let paths = NSSearchPathForDirectoriesInDomains(.DocumentDirectory, .UserDomainMask, true)
    let documentsDirectory = paths[0]
    return documentsDirectory
}

Simple approach, convert UIImages to NSData. Then add image data’s into an NSArray. Then save the NSArray into UserDefault. When retrieving the NSArray from UserDefault,use ImageWithData method to render UIImage from the NSArray’s each elements. This is the easiest process if you really one to use UserDefaults for your purpose. Try this yourself.

That's really bad idea if you really going to do that. You should save image in DocumentDirectory and save images name in NSUserDefaults.

func saveImages(images:[UIImage]) {

     let fileManager = FileManager.default
     let path = (NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true)[0] as NSString) 
     var imagesNames = [String]()


    do {

        if !fileManager.fileExists(atPath: path as String){
            try fileManager.createDirectory(atPath: path as String, withIntermediateDirectories: true, attributes: nil)
        }

     for (index,image) in images.enumarated() {
        let imageName = "Image\(index).jpg"
        let imageData = UIImageJPEGRepresentation(image, 1.0)
        if fileManager.createFile(atPath: paths.appending("/\(file)") as String, contents: imageData, attributes: nil) {
         imagesNames.append(imageName)
        }
      }
     let storage = UserDefaults.standard
     storage.set(imagesNames, forKey: "imagesArray")
     storage.synchronize()

    }catch{
        //Throw Error
    } 
}