Add caption to img title tag in wordpress

I'm trying to add the caption to the image title tag in wordpress so the lightbox I'm using with display the caption, since all it shows is the title tag. I've added $caption as well as many other variations borrowed form the caption shortcode. Any suggestions?

function get_image_tag($id, $alt, $title, $align, $caption, $size='medium') {

    list( $img_src, $width, $height ) = image_downsize($id, $size);
    $hwstring = image_hwstring($width);


    $class = 'align' . esc_attr($align) .' size-' . esc_attr($size) . ' wp-image-' . $id;
    $class = apply_filters('get_image_tag_class', $class, $id, $align, $size);

    $html = '<img src="' . esc_attr($img_src) . '" alt="' . esc_attr($alt) . '" title=" ' . esc_attr($title).' | '. esc_attr($content).'" '.$hwstring.'class="'.$class.'开发者_开发百科" />';

    $html = apply_filters( 'get_image_tag', $html, $id, $alt, $title, $align, $caption, $size );

    return $html;
}

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To add caption to the images being displayed in lightbox.Follow the below steps:


- Go to admin dashboard and click the library,it will list out all uploaded 
  pictures used for lightbox.Then click on the image for which you want to give caption
  Then,that image properties will appear in that caption field is there.
                                [OR]

- You can include caption while adding image itself.For that click the media tab -> add 
  new.Upload New Media will open,in that click select files and load the image from your 
  local machine.After the image is uploaded.Below that image you will see the caption 
  property.