I am trying to create a monthly checklist
When an item on the checklist is completed, I want to insert a signature image - (.jpg file)

Is there a way to:

Prompt for a password when the user tabs into a cell

and

Based upon the password, insert the corresponding signature image.

Example:

John Doe tabs into a cell, it prompts for his password, he enters the password and the image of his signature appears.

Jane Doe tabs into a cell, it prompts for her password, he enters the password and the image of her signature appears.

A person should not be able to cut and paste the signature image after it is inserted.
There maybe multiple signatures on the sheet through the course of a month.