According to regulations, which item is mandatory for a valid ID when purchasing SLCPs?

For a valid ID when purchasing Scheduled Listed Chemical Products (SLCPs), having a photograph of the individual is essential. This requirement acts as a means of verifying the identity of the purchaser, ensuring that they are who they claim to be. The photograph on the identification makes it harder for individuals to make purchases using another person's identity, thus supporting regulations designed to monitor and control access to products that can be used in the illicit manufacture of controlled substances.

In the context of purchasing SLCPs, other options like proof of employment, a recent utility bill, or a digital signature may not provide sufficient verification of the individual's identity in a robust manner. These forms of identification do not inherently include a photo, which is a critical component for this particular regulation pertaining to security and identity verification. Thus, the presence of a photograph on the ID is what makes it a mandatory requirement in this scenario.