Security

This may not be a security question, but any help would be appreciated.

Contactless payments are a fast growing method and opportunity to donate to charity. These can qualify for Gift Aid ( a UK Tax Relief system) and so could be worth 25% more. However, there needs to be some method of identifying the donor. If some of the 16 digits of the credit card number could be captured and checked against a database whether the holder ( i.e. the donor) had previously registered then this would satisfy the tax requirements. Ideally a bar code would suffice, but this is not generally available on credit cards. I have considered scanning and OCR of the credit card. Is there any way that some of the card number could be captured. capturing 8 digits would give 10 million numbers which would be acceptable. Thank you