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\Bitrix\Main\EventManager::getInstance()->addEventHandler(
    "main",
    "OnAfterResizeImage",
    array(
        "Handlers",
        "checkBadPictures"
    )
);

class Handlers{
    public static function checkBadPictures(
        $file,
        $options,
        &$callbackData,
        &$cacheImageFile,
        &$cacheImageFileTmp,
        &$arImageSize
    ) {
        if (file_exists($cacheImageFileTmp)) {
            if (stripos($cacheImageFileTmp, 'jpg') !== false || stripos($cacheImageFileTmp, 'jpeg') !== false) {
                $maxColor = 251;
                $oldImg = imagecreatefromjpeg($cacheImageFileTmp);
                $sizes = getimagesize($cacheImageFileTmp);
                $newImg = imagecreatetruecolor($sizes[0], $sizes[1]);
                imagecopyresampled($newImg, $oldImg, 0, 0, 0, 0, $sizes[0], $sizes[1], $sizes[0], $sizes[1]);
                $colorWhite = imagecolorallocate($newImg, 255, 255, 255);
                for ($y = 0; $y < ($sizes[1]); ++$y) {
                    for ($x = 0; $x < ($sizes[0]); ++$x) {
                        $colorat = imagecolorat($newImg, $x, $y);
                        $r = ($colorat >> 16) & 0xFF;
                        $g = ($colorat >> 8) & 0xFF;
                        $b = $colorat & 0xFF;

                        // Если цвет пикселя нас не устраивает, заменяем его на белый
                        if (($r >= $maxColor && $g >= $maxColor && $b >= $maxColor)) {
                            imagesetpixel($newImg, $x, $y, $colorWhite);
                        }
                    }
                }
                imagejpeg($newImg, $cacheImageFileTmp, 100);
            }
        }
    }
}