Why can the printed health code work, but the photos can't be developed?

In theory, health codes can only be effective and useful if they are scanned by mobile phones and then displayed in real time. ..... but in practical situations, such as students, or they don't have mobile phones, or schools don't allow them to bring mobile phones, so it is difficult for them to scan the code in real time. In addition, for example, the elderly can't scan the code with smart phones, and the health code can't be scanned in real time with mobile phones ... For these people, you can also let others scan the code and then use them to print or develop the health code. ...

As for printing the work and not taking photos, it may be because the printed health code is considered as the direct printing of the source file, which can better prove its authenticity. ...

In fact, in the above circumstances, it is actually more convenient to print out the health code ... Many places have printers to print out the health code. This operation is very simple ... it's much simpler than taking pictures and then developing them ... After all, there are very few photo studios now. ...

Therefore, if you have the conditions, it is the best choice to scan the health code in real time with your mobile phone ... If you don't have the conditions, scan the code and print it out, or ...