A Look-up field can look up to what?

What statement is true regarding a custom field formula?

Lookup fields allow users to select a record from another object during data entry, creating a parent- child relationship.

Is identity confirmation necessary if a user's IP address is known and browser cookie exists?

Northern Trail Outfitters has hired interns to enter Leads Into Salesforce and has requested a way to identify these new records from existing Leads.
What approach should an administrator take to meet this requirement?