Hi Jesper,
We have no plans to allow users to point to an image on a url link.
The image for WebMeeting is easily changeable by going to the Management Console > Settings > Conferences and selecting the image you'd like to use for WebMeeting branding.
Again just FYI, you can use any image type in this field. That includes .gif extensions which would allow you to add a small animation of your company's logo for example.