Blocking Nude Images using PHP

Wikipedia reads, "Nudity, or nakedness, is the state of wearing no clothing. The wearing of clothing is a predominantly human characteristic arising from functional needs such as protection from the elements and from cold temperatures, after the loss of body hair, and migration to colder regions. The amount of clothing worn depends on functional considerations, such as a need for warmth, as well as social circumstances. In some situations, a minimum amount of clothing or none at all may be considered socially acceptable, while in others much more clothing may be expected. Social considerations involve issues of modesty, decency and social norms, besides other considerations, and these may depend on the context. There may also be legal considerations." Suppose, you are hosting a webpage/service which allows users to upload images and a user uploads a nude image to your server and your website is not listed under the porn category, then it can be illegal. To prevent this, you'll need a PHP class named 'ImageFilter'. The function in this class returns a score in terms of percentage. If the score is greater than 60%, the image is considered to be nude. The class goes as follows:

imagefilter.php

<?php
class ImageFilter
{                              #R  G  B
    var $colorA = 7944996;     #79 3B 24
    var $colorB = 16696767;    #FE C5 BF

    var $arA = array();
    var $arB = array();
    
    function ImageFilter()
    {
        $this->arA['R'] = ($this->colorA >> 16) & 0xFF;
        $this->arA['G'] = ($this->colorA >> 8) & 0xFF;
        $this->arA['B'] = $this->colorA & 0xFF;
        
        $this->arB['R'] = ($this->colorB >> 16) & 0xFF;
        $this->arB['G'] = ($this->colorB >> 8) & 0xFF;
        $this->arB['B'] = $this->colorB & 0xFF;
    }
    
    function GetScore($image)
    {
        $x = 0; $y = 0;
        $img = $this->_GetImageResource($image, $x, $y);
        if(!$img) return false;

        $score = 0;
        
        $xPoints = array($x/8, $x/4, ($x/8 + $x/4), $x-($x/8 + $x/4), $x-($x/4), $x-($x/8));
        $yPoints = array($y/8, $y/4, ($y/8 + $y/4), $y-($y/8 + $y/4), $y-($y/8), $y-($y/8));
        $zPoints = array($xPoints[2], $yPoints[1], $xPoints[3], $y);

        for($i=1; $i<=$x; $i++)
        {
            for($j=1; $j<=$y; $j++)
            {
                $color = imagecolorat($img, $i, $j);
                if($color >= $this->colorA && $color <= $this->colorB)
                {
                    $color = array('R'=> ($color >> 16) & 0xFF, 'G'=> ($color >> 8) & 0xFF, 'B'=> $color & 0xFF);
                    if($color['G'] >= $this->arA['G'] && $color['G'] <= $this->arB['G'] && $color['B'] >= $this->arA['B'] && $color['B'] <= $this->arB['B'])
                    {
                        if($i >= $zPoints[0] && $j >= $zPoints[1] && $i <= $zPoints[2] && $j <= $zPoints[3])
                        {
                            $score += 3;
                        }
                        elseif($i <= $xPoints[0] || $i >=$xPoints[5] || $j <= $yPoints[0] || $j >= $yPoints[5])
                        {
                            $score += 0.10;
                        }
                        elseif($i <= $xPoints[0] || $i >=$xPoints[4] || $j <= $yPoints[0] || $j >= $yPoints[4])
                        {
                            $score += 0.40;
                        }
                        else
                        {
                            $score += 1.50;
                        }
                    }
                }
            }
        }
        
        imagedestroy($img);
        
        $score = sprintf('%01.2f', ($score * 100) / ($x * $y));
        if($score > 100) $score = 100;
        return $score;
    }
    
    function GetScoreAndFill($image, $outputImage)
    {
        $x = 0; $y = 0;
        $img = $this->_GetImageResource($image, $x, $y);
        if(!$img) return false;

        $score = 0;

        $xPoints = array($x/8, $x/4, ($x/8 + $x/4), $x-($x/8 + $x/4), $x-($x/4), $x-($x/8));
        $yPoints = array($y/8, $y/4, ($y/8 + $y/4), $y-($y/8 + $y/4), $y-($y/8), $y-($y/8));
        $zPoints = array($xPoints[2], $yPoints[1], $xPoints[3], $y);

        for($i=1; $i<=$x; $i++)
        {
            for($j=1; $j<=$y; $j++)
            {
                $color = imagecolorat($img, $i, $j);
                if($color >= $this->colorA && $color <= $this->colorB)
                {
                    $color = array('R'=> ($color >> 16) & 0xFF, 'G'=> ($color >> 8) & 0xFF, 'B'=> $color & 0xFF);
                    if($color['G'] >= $this->arA['G'] && $color['G'] <= $this->arB['G'] && $color['B'] >= $this->arA['B'] && $color['B'] <= $this->arB['B'])
                    {
                        if($i >= $zPoints[0] && $j >= $zPoints[1] && $i <= $zPoints[2] && $j <= $zPoints[3])
                        {
                            $score += 3;
                            imagefill($img, $i, $j, 16711680);
                        }
                        elseif($i <= $xPoints[0] || $i >=$xPoints[5] || $j <= $yPoints[0] || $j >= $yPoints[5])
                        {
                            $score += 0.10;
                            imagefill($img, $i, $j, 14540253);
                        }
                        elseif($i <= $xPoints[0] || $i >=$xPoints[4] || $j <= $yPoints[0] || $j >= $yPoints[4])
                        {
                            $score += 0.40;
                            imagefill($img, $i, $j, 16514887);
                        }
                        else
                        {
                            $score += 1.50;
                            imagefill($img, $i, $j, 512);
                        }
                    }
                }
            }
        }
        imagejpeg($img, $outputImage);

        imagedestroy($img);

        $score = sprintf('%01.2f', ($score * 100) / ($x * $y));
        if($score > 100) $score = 100;
        return $score;
    }
    
    function _GetImageResource($image, &$x, &$y)
    {
        $info = GetImageSize($image);
        
        $x = $info[0];
        $y = $info[1];
        
        switch( $info[2] )
        {
            case IMAGETYPE_GIF:
                return @ImageCreateFromGif($image);
                
            case IMAGETYPE_JPEG:
                return @ImageCreateFromJpeg($image);
                
            case IMAGETYPE_PNG:
                return @ImageCreateFromPng($image);
                
            default:
                return false;
        }
    }
}
?>

And, how to use this class? It's usage is explained in the code below:

<?php
require_once('imagefilter.php');
$filter = new ImageFilter;
$score = $filter->GetScore($uploaded_image);
if(isset($score)) {
    if($score >= 60) {
        echo "The image you have uploaded has scored ".$score."% and an image scoring more than 60% is considered as a nude image :(";
    }
}
?>