Yawcam

I have a logitech quickcam fusion and dump each 30seconds an image. This image is only actual when I have the preview screen shown. If not it has a hughe delay (few seconds).

What's the cause of it, and how can I solve it.

If I run it as a service it has the same delay.

Can't really say, but it sounds like it takes some time for the camera to initialize.
Try turning the motion detection on with all its actions turned off & set sensitivity
to 0% & tolerance to 100% (so it never triggers). That should keep the camera
"awake" & eliminate the delay.