Compares two images to see if they have identical content

gistfile1.txt

func UIImageEqualToImage(image1: UIImage, _ image2: UIImage, ciContext: CIContext? = nil) -> Bool
{
    guard let
        ciImage1 = CIImage(image: image1),
        ciImage2 = CIImage(image: image2) where image1.size == image2.size else
    {
        return false
    }
 
    let ctx = ciContext ?? CIContext()
    
    let difference = ciImage1.imageByApplyingFilter("CIDifferenceBlendMode",
            withInputParameters: [kCIInputBackgroundImageKey: ciImage2])
        .imageByApplyingFilter("CIAreaMaximum",
            withInputParameters: [kCIInputExtentKey: CIVector(CGRect: ciImage1.extent)])
    
    let totalBytes = 4
    let bitmap = calloc(totalBytes, sizeof(UInt8))
    
    ctx.render(difference,
        toBitmap: bitmap,
        rowBytes: totalBytes,
        bounds: difference.extent,
        format: kCIFormatRGBA8,
        colorSpace: nil)
    
    let rgba = UnsafeBufferPointer<UInt8>(
        start: UnsafePointer<UInt8>(bitmap),
        count: totalBytes)
    
    return rgba[0] == 0 && rgba[1] == 0 && rgba[2] == 0
}

This is maybe a nice solution, but it's not the best solution.

See this project for a comparison: https://github.com/FlexMonkey/ImageCompareDemo