Students search for the answer key to bypass the learning. However, a properly designed mystery picture has a "feedback loop." If you blindly copy an answer key, you may reveal the picture, but you will fail the unit test. The picture is a study tool, not the final assessment.
One of the most powerful aspects of this tool is the self-checking nature of the activity. In a traditional worksheet, a student might answer all 20 questions incorrectly and not realize it until the teacher hands it back three days later. By that time, the learning moment has passed. With a mystery picture, if a student answers a question wrong, the color they apply will likely clash with the surrounding pattern, or the resulting image won't make sense (e.g., a "cell" might look like a blob). This alerts the student immediately, prompting them to re-evaluate their answer. biology review mystery picture answer key