附加base64 img时获取黑色图片

我正在尝试发送带有图片附件的电子邮件。我可以发送电子邮件，但是显示图片（仅黑色）没有成功。所述php正在接收一个base64字符串，它是一个图像。另外我想这样做没有任何存储或写入服务器上的任何东西。有没有办法做到这一点？
这是个什么php样子。

   <?php 
    $base64 = $_POST['dataURL'];
    //define the receiver of the email 
    $to = '[email protected]'; 
    //define the subject of the email 
    $subject = 'Test email with attachment'; 
    //create a boundary string. It must be unique 
    //so we use the MD5 algorithm to generate a random hash 
    $random_hash = md5(date('r', time())); 
    //define the headers we want passed. Note that they are separated with \r\n 
    $headers = "From:Francisco Granado\r\nReply-To: [email protected]"; 
    //add boundary string and mime type specification 
    $headers .= "\r\nContent-Type: multipart/mixed; boundary=\"PHP-mixed-".$random_hash."\""; 
    //read the atachment file contents into a string,
    //encode it with MIME base64,
    //and split it into smaller chunks
    $attachment = base64_decode($base64); 
    //define the body of the message. 
    ob_start(); //Turn on output buffering 
    ?> 
    --PHP-mixed-<?php echo $random_hash; ?>  
    Content-Type: multipart/alternative; boundary="PHP-alt-<?php echo $random_hash; ?>" 

    --PHP-alt-<?php echo $random_hash; ?>  
    Content-Type: text/plain; charset="iso-8859-1" 
    Content-Transfer-Encoding: 7bit

    This email have attached a image file 
    For SED_WE analysis purposes. 

    --PHP-alt-<?php echo $random_hash; ?>  
    Content-Type: text/html; charset="iso-8859-1" 
    Content-Transfer-Encoding: 7bit

    <h1>SED_WE</h1>
    <p>This email have attached a image file </p> 
    <p>For SED_WE analysis purposes.</p> 

    --PHP-alt-<?php echo $random_hash; ?>-- 

    --PHP-mixed-<?php echo $random_hash; ?>  
    Content-Type: image/jpeg; name="attachment.jpeg"  
    Content-Transfer-Encoding: base64  
    Content-Disposition: attachment  

    <?php echo $attachment; ?> 
    --PHP-mixed-<?php echo $random_hash; ?>-- 

    <?php 
    //copy current buffer contents into $message variable and delete current output buffer 
    $message = ob_get_clean(); 
    //send the email 
    $mail_sent = @mail( $to, $subject, $message, $headers ); 
    //if the message is sent successfully print "Mail sent". Otherwise print "Mail failed" 
    echo $mail_sent ? "Mail sent" : "Mail failed"; 
   ?>

这也是我的js：

$(document).ready(function (e) {
    var imgBase64;
    function imgToBase64(url, callback, outputFormat) {
        var canvas = document.createElement('CANVAS'); //Creates variable containing canvas in the DOM
        var canvas_context = canvas.getContext('2d'); //Creates canvas environment (context) in 2 dimensions 
        var img = new Image; // new Image instance
        img.crossOrigin = 'Anonymous'; //Cross origin textures from other URL's are permitted (see http://blog.chromium.org/2011/07/using-cross-domain-images-in-webgl-and.html) for more information
        console.log('ON LOAD IMG');
        //Image load trigger, encode image into base64
        img.onload = function () {
            //Determine canvas height and width 
            canvas.height = img.height;
            canvas.width = img.width;
            console.log('Canvas info:\n Height: ' + canvas.height + '\n Width: ' + canvas.width);
            //Draws the image raw format 
            canvas_context.drawImage(img, 0, 0);
            var dataURL = canvas.toDataURL(outputFormat || 'image/png'); //THIS IS WHERE THE MAGIC HAPPENS (img encode to base64)
            //imgBase64 = dataURL;
            $('#show-picture').attr('src', dataURL); //Change source of the #show-picture image tag to the base64 string to show preview to user 
            console.log(dataURL);
            callback.call(this, dataURL); //Callback function @param {dataURL} 
            // Clean up
            canvas = null;
        };
        img.src = url;
    }

    //Reads the path to the picture for a preview 
    function readURL(input) {
        if (input.files && input.files[0]) { //if file exist
            var reader = new FileReader(); //new instance of the file reader

            reader.onload = function (e) { //when the reader loads the chosen file...
                imgToBase64(e.target.result, function (dataURL) { //..then the is converted 
                    setDataURL(dataURL);
                });
            }
            reader.readAsDataURL(input.files[0]);
        }
    }

    function setDataURL(dataURL){
        imgBase64 = dataURL;
        console.log('setDataUrl=>'+imgBase64);
    }



    $('#take-picture').change(function () {
        readURL(this);
        console.log('ONLOAD'+imgBase64);
    });

    $('#uploadImgBtn').on('click',function(){
        var base64String= imgBase64.replace(/data:image[^;]+;base64,/,'');
        console.log('base64string'+base64String);
        $.post('php/mailer.php',base64String,function(data){alert('Success!'); console.log('response: '+data)});
    });

});

PS：我尝试了与其他文章不同的方法，但是没有成功，或者它们写在服务器上，这也是我第一次使用php，因此欢迎任何好的建议。