比较两个图像的内容，看它们是否相似

Question

我需要比较两个图像的内容，看它们是否相似。我读过有关Graphics Content，OpenCV和Hashes-Check的内容，但我无法弄清楚如何做到这一点。问题是我有一个缩略图，我必须比较全尺寸图像，看看它们是否相似，所以我不认为我必须检查图像的高度和宽度，因为它们的尺寸不一样。我读到了绘制图像内容并比较其字节但我不知道如何继续。 这是我的代码：

let url1 = NSData(contentsOf: URL(string: "https://url1.com/url1.jpg")!)
    let url2 = NSData(contentsOf: URL(string: "https://url2.com/url2.jpg")!)
    let img1 = UIImage(data: url1 as! Data)
    let img2 = UIImage(data: url2 as! Data)

    func convertCIImageToCGImage(inputImage: CIImage) -> CGImage! {
        let context = CIContext(options: nil)
        if context != nil {
            return context.createCGImage(inputImage, from: inputImage.extent)
        }
        return nil
    }
    var ciImage = CIImage(image: img1!)
    let cgImage = convertCIImageToCGImage(inputImage: ciImage!)

    func createARGBBitmapContext(inImage: CGImage) -> CGContext {
        var bitmapByteCount = 0
        var bitmapBytesPerRow = 0

        //Get image width, height
        let pixelsWide = inImage.width
        let pixelsHigh = inImage.height

        // Declare the number of bytes per row. Each pixel in the bitmap in this
        // example is represented by 4 bytes; 8 bits each of red, green, blue, and
        // alpha.
        bitmapBytesPerRow = Int(pixelsWide) * 4
        bitmapByteCount = bitmapBytesPerRow * Int(pixelsHigh)

        // Use the generic RGB color space.
        let colorSpace = CGColorSpaceCreateDeviceRGB()

        // Allocate memory for image data. This is the destination in memory
        // where any drawing to the bitmap context will be rendered.
        let bitmapData = malloc(bitmapByteCount)

        // Create the bitmap context. We want pre-multiplied ARGB, 8-bits
        // per component. Regardless of what the source image format is
        // (CMYK, Grayscale, and so on) it will be converted over to the format
        // specified here by CGBitmapContextCreate.
        let context = CGContext(data: bitmapData, width: pixelsWide, height: pixelsHigh, bitsPerComponent: 8, bytesPerRow: bitmapBytesPerRow, space: colorSpace, bitmapInfo: CGImageAlphaInfo.premultipliedFirst.rawValue)

        // Make sure and release colorspace before returning
        return context!
    }

    let context = createARGBBitmapContext(inImage: cgImage!)
    context.draw(img1!.cgImage!, in: CGRect(x: 0.0,y: 0.0,width: img1!.size.width,height: img1!.size.height))