Ideally make the image 1000*1000 pixels. Try to link parts of the picture to edges at 1/3 intervals that makes them look better when joined.
Optional: send a short audio commentary
And as a minimal formality, please copy and paste the following statement into your email: "I consent to Tim Jones reproducing and displaying this picture (and attached audio if relevant) individually, alongside, or joined to the work of others in the Exquisite Corpse of Science Project"