This is a just in case comment. Are you aware that search engine spider bots cannot read any text in images? That's why it's essential to have a blog title here > Settings > General Without it the search spiders will not index your site. It's also important that the blog title is the only H1 heading appearing on your page.
CSS is theme specific at wordpress.COM. Since there is no official Staff support for the CSS upgrade, and precious little Volunteer support, I recommend that you don’t buy the upgrade unless you have at least moderate understanding of HTML and CSS because you must be prepared to do the work on your own.
If you are considering purchasing the upgrade, you can go to Appearance > Edit CSS. There wordpress has provided a preview function where you can try before you buy.
If you do purchase the upgrade be sure to read this article before starting your editing > http://csswiz.wordpress.com/2009/10/15/if-you-have-the-wp-com-css-upgrade/ and then search the forum as CSS editing such as this have been dealt with before in other forum threads http://en.forums.wordpress.com/topic/remove-page-title-for-homepage-in-bueno?replies=8#post-562666