Does a valid CRC mean the payment is safe?
It only means the code's text was not corrupted or edited after it was generated. It is not a check that the recipient is who they claim to be, so it is always worth checking the shown name and city against who you expect to pay.
Can I scan the PIX code from an image, without using the camera?
Yes, the tool has an image upload mode that accepts dragging a file, picking one from the file browser, or pasting from the clipboard, useful when the QR code arrived as a screenshot in a chat.
Is the payment made through this tool?
No, the tool only decodes and checks the code, it does not process payments. The copy PIX code button is meant for pasting into your own banking app, where the payment is actually confirmed.