probably something in your theme interfering with it
i resized the pic and tested, it works fine.
PHP Code:
<p align="center"><img alt="image" src="http://media.tumblr.com/e3a9c3ef7442565cf15821ac0aac5690/tumblr_inline_mw6zrhgxgt1srtovh.jpg" width=42 height=42 /></p>