Scan document from files on web gui and smartphone apps

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This is a request for web gui and smartphone apps, I don't know where to post it (need I to create 3 feature requests: web, ios and android?) so I'm posting it here, please move this feature requeste if needed.

Is your feature request related to a problem? Please describe.
I have/receive many documents in image format on my email/im/computer that I would like to convert to documents in the same way like scan document from camera do.

I can see that Nextcloud apps can scan documents from camera, why is not possibile to do the same way with files (example: images)?

Describe the solution you'd like
Use the same workflow (with the possibility to stretch corners) as "scan document from camera" but giving the chance to select files like pdf and images. Why pdf? Because usually people create pdf from image without before stretching corners.

Describe alternatives you've considered
The alternative is display those images/pdf on another screen and then use scan document from camera, I really don't want to do it.

Additional context
I think that this is a simple task to do because we need only the possibility to select if ne need to import a file/image or to use the camera.

Start by locating the existing camera document-scanning workflow in the web, iOS, and Android apps. Determine how file and PDF selection can enter that workflow and preserve corner-stretching; done means the requested import flow works across the relevant clients.