Leopold,
it is very easy to do in the current version 7:
1. Select an area, either rectangular, freehand, or draw a shape (e.g. circle) and right-click to convert it to selection.
2. Click "Copy" button to copy this selection, then click on the image, but outside of selection, to cancel this selection.
3. Now apply the filter you want, e.g. mosaic, to the whole image, as there is no selection at the moment.
4. Press Ctrl+V or any other button/key combination to paste what you copied in step 2. It copies _exactly_ at the same position it was originally at. You have your effect as you wanted.
Make sure you use the latest v7 of HyperSnap for this. Here is what I just did - I used brightness control to dim the entire image except the circle in the middle:
Greg
post edited by Support - 2012/05/14 18:28:58