Try this:
add_filter( 'excerpt_more','tu_image_read_more', 100 );
add_filter( 'the_content_more_link','tu_image_read_more', 100 );
function tu_image_read_more()
{
$link = get_permalink();
$title = get_the_title();
return '<a href="' . $link . '" title="' . $title . '"><img class="read-more-image" src="http://playerwags.com/wp-content/uploads/2014/07/read-more-logo23.png" alt="read more" /></a>';
}
Then add this CSS:
.entry-content .read-more-image,
.entry-summary .read-more-image {
width: auto;
}
Hope this helps ๐