Carmen Castrejon's CD-and-pencil mirror turned a laptop webcam into a document camera

When COVID-19 pushed classes online in 2020, teachers who taught by writing on a board could not show working solutions as they explained them. A laptop webcam points at the person in front of the screen, not at the desk, and the reporting noted that teachers and lecturers 'may frequently need to show workings as they are being written' without fancy equipment.

US teacher Carmen Castrejon shared a Facebook post on Sep. 3, 2020 explaining a low-tech rig: tape a pencil to the back of the laptop cover, aligned with the camera; rest a CD on the pencil with its reflective side facing down; tape a coin on the CD as a weight. Whatever lies in the keyboard area of the laptop now appears on camera, and removing the CD returns the view to the teacher's face.

The hack works by changing where the camera looks instead of buying a new one: the CD is a mirror that bends the webcam's line of sight down to the paper in the keyboard area, the pencil is the mount that holds it at the right height, and the coin keeps the reflective surface at the right tilt. Because the parts are everyday objects and the assembly takes seconds, any teacher could copy it and undo it between lessons.

The post went viral, with more than 24,000 shares after it was reposted by the Facebook page HugotMaestra, and Mothership in Singapore covered the trick on Sep. 5, 2020. Posted to Hacker News on Sep. 13, the story drew 704 points and 267 comments, where readers swapped the CD for compact mirrors and traded setup tips, confirming the transferable idea was the mirror, not the disc.

Redirect the laptop camera with a CD mirror, not new gear

It solves the camera, not the classroom: a cheap reflective surface bends the webcam's line of sight onto the desk, so the teacher writes naturally instead of holding paper up to the lens.

Every household object does an optical job: the pencil mounts the mirror at camera height, the coin counterweights the tilt, and the CD is a mirror already present in most homes.

It costs nothing and reverses in seconds: four items and four steps, and lifting the CD restores the face-to-face view, so there is no risk in trying it before a live class.

Simplicity made it viral and improvable: 24,000+ shares and a 704-point Hacker News thread carried the idea to other teachers, who adapted it with compact mirrors rather than CDs.

When the right tool is missing, change the path, not the goal: a mirror redirects an existing camera to a new subject, and a four-object household rig is copyable by anyone.

Castrejon's post was shared more than 24,000 times after the Facebook page HugotMaestra reposted it, and Mothership, a Singapore outlet, covered the trick on Sep. 5, 2020. When the story hit Hacker News on Sep. 13, it drew 704 points and 267 comments; readers tested alternatives such as hinged compact mirrors draped over the laptop lid and warned against compacts still full of makeup, confirming the principle, not the CD, was the hack. No product, company or brand came out of it: the fix stayed a free technique for teachers who could not buy their way out of the lockdown.