Not impossible, but hard. It's diagonally symmetrical. All the quarters have the same pattern, but adjoining quarters are inverted(a black space becomes a white space). So top left and bottom right are the same but mirrored(except for a missing dot near the bottom right corner).
Uff - got it! Difficult, but solvable. The two 25 lines are the axis. Left top part is mirrored to the right top part, but inverse (white changes into black, black changes into white), and mirrored to lower left part, also inverse. The top left part is the same than the lower right part; also the top right part is the same than the lower left part. Very clever, Char :-)