You would need to remove their address/contactkey from your system as well to stay GDPR compliant. The Marketing Cloud will allow the contact key back into the system after it has been fully deleted. This includes having the device register to the Marketing Cloud from the SDK.
If you have access to Contact Builder (including a.o. Data Designer seen below), you do have the "new" Contacts structure.
You can find Contact Builder by following these steps:
Log in to Marketing Cloud.
Locate the primary navigation bar.
Hover over Audience Builder.
Click Contact Builder.
Indeed only very old instances of Marketing Cloud are not ...
I think you are looking to read business cards automaticallly and store the info in to Salesforce Objects. For that you can use the OCR feature offered by Google Cloud Vision API.
The Vision API can detect and extract text from images. There are two annotation features that support optical character recognition (OCR):
TEXT_DETECTION detects and extracts ...