You can record a CLICK on the image to get the right locator, and then, after recording, replace the CLICK command with storeImage.
Technically storeimage does not download the image, but takes a screenshot of it. But for most cases that should be the same, or is even better (e. g. on sites that block image downloads or captcha images).
You can “download” the image screenshot from inside the Kantu “Screenshot” tab to your hard drive with a second command: LocalStorageExport
StoreImage | locator | screenshotname.png
LocalStorageExport | screenshotname.png