Gonna guess those are Gravatar images? Sounds like something's down somewhere between you and Gravatar. We've had a couple reports to that effect earlier this week, but unfortunately there's not much we can do.
This is caused by a combination of things on your end, most likely fonts installed on your operating system, your browser's choice of rendering, and the zoom level of the page. The site has no control over these things. Zooming especially is not supported by SE.
For reference, the font-family of the site prefers Arial, then "Helvetica Neue",...