check this. I saw it on zdnet.com
Take PSO Screenshots
This requires an extra DC controller plugged into port D, and an empty VMU in that controller. When you want to take the screenshot, press Start, A and X at the same time. A countdown will appear, which is the file being saved to your VMU. After the shot is taken, go to this site, using your Dreamcast browser:
And you should now have a great image of your PSO game! Please note that PlanetWeb v1.0 doesn't allow you to upload VMU images.
can someone try this and see if it works?