custom submit button in a form not showing image

hi there!
i have a form with a submit buttom to subit comments.
I wanted to custom the buttom using an image, it works but the image is not showing, it shows sth like this: http://www.underconsideration.com/brandnew/archives/google_broken_image_00_a_logo.gif

here is my code:

<form action="<?php echo get_option('siteurl'); ?>/wp-comments-post.php" method="post" id="comment_form">
	<label for="comment">Post a comment</label>
	<textarea name="comment" id="comment" cols="75%" rows="4" tabindex="1"></textarea>
	<ul id="comment_label">
		<li>
			<label for="author">Name <span class="required"><?php if($req) echo "*required"; ?></span></label>
		</li>
		<li>
			<label for="email">E-mail <span class="required"><?php if($req) echo "*required"; ?></span></label>
		</li>
		<li>
			<label for="submit">Submit </label>
		</li>
	</ul>
	<ul id="comment_box">
		<li>
			<input type="text" name="author" id="author" value="<?php echo $comment_author; ?>" size="28" tabindex="2" />
		</li>
		<li>
			<input type="text" name="email" id="email" value="<?php echo $comment_author_email; ?>" size="28" tabindex="3" />
		</li>
		<li id="submit_li">	

			<input type="image" name="submit" id="submit" src="images/fineblackline_blogopen_submitbutton.png" tabindex="4" />
			<input type="hidden" name="comment_post_ID" value="<?php echo $id; ?>" />
		</li>
	</ul>
	<?php do_action('comment_form', $post->ID); ?>
</form>

What am i doing wrong?

this is my css:

#comment_form{
	margin-top: 7%;
}
label[for=comment]{
	font-family: 'Sverige';
	font-size: 1.7em;
	line-height: 1.3em;
}
textarea#comment{
	font-family: 'Eraslght';
	font-size: 1.1em;
	line-height: 1.4em;
}
label[for=submit]{
	font-family: 'Sverige';
	color: #FF2562;
	/*padding-left: 2%;*/
}
#comment_form ul li{
	display: inline;
}
input[type=text]{
	font-family: 'Eraslght';
	font-size: 0.6em;
	line-height: 1.4em;
}

.required{
	font-family: 'Eraslght';
	font-size: 0.6em;
	line-height: 1em;
}
ul#comment_label{
	margin-top: 3%;
	font-family: 'Sverige';
	font-size: 1.7em;
	line-height: 1.3em;
	padding: 0;
}
ul#comment_label li{
	margin: 0 12% 0 0;
}
ul#comment_box{
	margin-top: 1%;
	font-family: 'Sverige';
	font-size: 1.7em;
	line-height: 1.3em;
	padding: 0;
}
ul#comment_box li{
	margin: 0 0 0 0;
	height: 37px;
}
ul#comment_box li#submit_li{
	width: 47px;
	height: 37px;
}