Hint: If you look at the top five squares you will notice a pattern which should help you work out which black square should be removed from the next 5by5 square.
Wow, only 6 solutions, I wouldn't have bet it. To find the good one, you just have to know that R22C1 and R23C17 are black. But it demands some difficult tricks and I'm not able to discribe it in English (in french, it's called "principe d'alternance"). It will be great if you test your productions and make them easier in the future.
EDIT : Oh, I didn't see (and didn't understand Poppy's comment), the picture is a game which helps you to finish. You partially solve the hanjie, then you're stuck... But, you understand the picture and finally you can finish. Very ingenious, thank you Cureshut.
The puzzle has multiple possible solutions; however, if you pick up the pattern you can figure out how to solve the puzzle in one attempt. Thank you for the fun puzzle!
I was charmed by this one. It isn't solvable by normal hanjie rules, but once you see the pattern and apply it to the remaining squares, it can be conquered.