Replacing Blog Title With Image in Twenty Eleven Theme

Hi. I’m really hoping that some of you are familiar with the Twenty Eleven theme that comes with self-hosted versions of WP. It probably even comes in the other WP. Anyway, I just want to replace the blog title with a small image logo.

You can find the blog here.

There’s just one problem. I already tried online suggestions with replacing the header text field with an img tag. While it works, it also gives me an inflated gigantic version of the image.

I’m moderately good at PHP and HTML5, but I’m not so well versed in CSS. Not sure how I should take this.