I have used the below code to send an attachment image..
You can try this one.
            <?php
            if (isset($_POST['submit'])) {
            $headers = "From: abc@example.com  mailer \r\n";
            $message .= $_POST['message'];  
                /* GET File Variables */ 
            $tmpName = $_FILES['attachment']['tmp_name']; 
            $fileType = $_FILES['attachment']['type']; 
            $fileName = $_FILES['attachment']['name']; 
            if (file_exists($tmpName)) { 
              /* Reading file ('rb' = read binary)  */
              $file = fopen($tmpName,'rb'); 
              $data = fread($file,filesize($tmpName)); 
              fclose($file); 
              /* a boundary string */
              $randomVal = md5(time()); 
              $mimeBoundary = "==Multipart_Boundary_x{$randomVal}x"; 
              /* Header for File Attachment */
              $headers .= "\nMIME-Version: 1.0\n"; 
              $headers .= "Content-Type: multipart/mixed;\n" ;
              $headers .= " boundary=\"{$mimeBoundary}\""; 
              /* Multipart Boundary above message */
              $message = "This is a multi-part message in MIME format.\n\n" . 
              "--{$mimeBoundary}\n" . 
              "Content-Type: text/plain; charset=\"iso-8859-1\"\n" . 
              "Content-Transfer-Encoding: 7bit\n\n" . 
              $message . "\n\n"; 
              /* Encoding file data */
              $data = chunk_split(base64_encode($data)); 
              /* Adding attchment-file to message*/
              $message .= "--{$mimeBoundary}\n" . 
              "Content-Type: {$fileType};\n" . 
              " name=\"{$fileName}\"\n" . 
              "Content-Transfer-Encoding: base64\n\n" . 
              $data . "\n\n" . 
              "--{$mimeBoundary}--\n"; 
            } 
            $to_user = "your emailid";
            $flgchk = mail("$to_user", "$subject", "$message", "$headers"); 
            //require_once ('./includes/functions_mail.php');
                if ($flgchk) {
                echo "<META HTTP-EQUIV=\"refresh\" CONTENT=\"2;url=forwardtoother.php?page=inbox.php\">";
                echo "Done, <br>";
                echo "Redirecting you to your <a href=\"?page=inbox.php\">Inbox</a>";
                }
                else
                {
                     echo "<META HTTP-EQUIV=\"refresh\" CONTENT=\"2;url=forwardtoother.php?page=inbox.php\">";
                echo "Failed to send email, <br>";
                echo "Redirecting you to your <a href=\"?page=inbox.php\">Inbox</a>";
                }
            } 
            ?>
            <form name="form1" method="post" action="" enctype="multipart/form-data">
            <table>
                <tr>
                <td width='20'><b>Select File:</b> </td>
                <td width='20'><input type="file" name="attachment"></td>
                </tr>
              <p><td width='20'>
                 <input type="reset" name="Submit2" value="Start Over." class="Submit"/></td><td>
                 <input type="submit" name="Submit" value="Send" class="Submit" /></td></tr></table>
              </p>
            </form>