Adding visuals will come to Napkin, but not very soon. A workaround that helps many users is...
a) take a photo with your phone, generate a sharable link (e.g. iCloud) and add the link to the note in Napkin.
b) take a photo, use your iPhones OCR function to identify the text (works even with handwritten notes) and send the transformed text to Napkin via iOS Shortcut or soon via Napkin Collect.
Let us know how it works and/or if you find a better solution. 🤓