I was browsing the ArcGIS API for Python documentation relating to Forms. Well, I thought I'd stumbled across hidden treasure. The excitement meter went into overdrive.
What got me excited I hear you ask? It looked like I could create a question for adding an attachment (image or signature)
Check out these links
FormAttachmentInput
FormImageInput
FormSignatureInput
So, I can add these elements to Form using the ArcGIS API for Python. I also found more information over on the WebMap Specification...
formAttachmentElement
formAttachmentInput
formSignatureInput
I created a WebMap with a simple form. Notice, you cannot create an entry for an attachment.

Now, watch the magic that happens when I manipulate the JSON based on the WebMap Specification to create an extra entry in the form for capturing an image with some manners (naming photos, number of photos to be collected min/max for examples)

Unfortunately, that is where the magic ends 😢
When you open in Field Maps we are met with "The form contains unsupported data".
Come on Esri, make Christmas come early and update Field Maps to work with the behind the scenes JSON.
Or perhaps these already work, and I'm missing something?