You will need four feed, named: image1, image2, hotnot1 and hotnot2. The first two of these are to store the images uploaded by each of the devices, and the other two are to store the responses by the other device.

On the Adafruit.io homepage, click the feeds tab (circled orange below), and then click New Feed (circled red).

This will open a dialog box where you can enter the name for the feed (image1). You can leave the description blank.

Repeat this another three times to create the remaining feeds named image2, hotnot1 and hotnot2.

By default, each entry in a feed can only be 1Kb, which is a bit small to store an image (even one that's going to be displayed on a 240x240 pixel screen). However, turning off history, one can store up to 100Kb, which is plenty for our needs.

In the feed list, click on image1, and then in the right-hand section you can click on Feed History and turn it off. Repeat this for image2.