There's not a way to upload an image, but you can attach an image to the lead activity. You will need to first upload the image to a place that allows image, such as a Google Drive, Dropbox, etc. You will need to copy the URL of the image.
Then go create a new task, and in the notes section. In the highlighted section above is the area to attach the image. Click on it.
Paste the image source URL into where it says "Source" and then click "Save"
The image will not show up in the Note
Click "Save" and then the image will show up in the notes section,