Concept is sound. I didn't like the feeling from the controls. Too much clicking and zooming in and out I think. I'm not sure what could be done better RE: that. Like maybe being able to use the keys to move around and not rely on the mouse placement at the edges of the screen to move the view.
I ended up clicking around the zoomed out picture when I was frustrated. Maybe let it linger more when finding an imp. I knew something changed but I didn't know what until it disappeared. So it would be nice to see a before and after or an after with like silhouettes or circles where the imps were after completing the picture.
Good job on the sound and music. Very relaxing even though I'm looking for nasty lil imps.