my idea is about detecting circles in the image
input will be low-res (ascii) image, where a player should detect a circle (possibly using Hough transform)
test cases may include detecting multiply circles, different size circles, crossing circles, not complete circles (arcs)
in one of the variants of puzzle player may be driving a spaceship and should detect circles on the starry sky to pass directly through the center of it, i.e. player must detect a distance to circle by its size and adjust position of his ship until it matches the center of every next detected circle before passing through it
thank you in advance!
For the first idea, doesn’t it look similar to the existing Music score puzzle?
i doubt that for a couple of reasons:
- i still have no access to 4 level puzzles (i did not solve 100% of three level 3 puzzles) so i can not read full task description, only draft. draft says that it is based on earlier doctor who puzzle, the gift, and that puzzle does not look like this. forum topic about that also does not give much info
- i also don’t think that this is really very hard puzzle, as stated
why the image processing task has word “music” in its name? my description of possible game based on solution also matches much better
thank you for the answer anyway, it shows me that i still have many intersting puzzles to solve here 
The puzzle is about scanning a music score : you recieve as input a bitmap version of the score (the possible inputs are on this page) and your program has to output the list of the notes in that score.
As I have not solved it, I cannot judge of whether it is really “very hard”, but it does look as such, at least. And your puzzle idea doesn’t sound much easier. 