Professional CAPTCHA Instruction Copy

I need concise, formal copy that guides users to type the exact letters or numbers they see in our CAPTCHA image. The text will sit beside the CAPTCHA field on our login and account sign-up screens, so it must be instantly clear, accessible, and authoritative without sounding cold.

Key points I must cover
• Explain the action: users must reproduce the characters shown, preserving case and spacing if required.
• Reinforce purpose briefly: confirm identity and keep accounts secure.
• Keep it compact: 25–35 words total split over one or two short sentences so it fits cleanly in our current UI.

Please deliver the final line(s) in plain text plus a note on character count.