What are the two ways to turn a photo into lines?

In the page toolbar, "From your photo:":

• Lines made on this computer: free and instant. Tone zones become outlines, with fine details and a frame. Best for simple subjects on a clean background (a pet, a house, a face).
• Redrawn by your image engine (best): your image engine redraws the photo as line art, keeping the subject recognizable and simplifying the background. One picture on your key; "Draw again" makes another. This choice is greyed out without an OpenAI or Gemini key. Once the redrawn version exists, switching between the two is free.