How can I make Chrome allow access to a webcam over http (not https)?

Yes, an admin can override the prompts with a policy.

VideoCaptureAllowedUrls

Patterns in this list will be matched against the security origin of the requesting URL. If a match is found, access to audio capture devices will be granted without prompt. NOTE: This policy is currently only supported when running in Kiosk mode.

On Windows, you create registry entries using regedit.

Software\Policies\Chromium\VideoCaptureAllowedUrls\1 = "http://www.example.com/"
Software\Policies\Chromium\VideoCaptureAllowedUrls\2 = "http://[*.]example.edu/"

On Linux you write the policies in a file:

mkdir -p /etc/opt/chrome/policies/managed
touch /etc/opt/chrome/policies/managed/test_policy.json

In test_policy.json:

{
  "VideoCaptureAllowedUrls": ["http://www.example.com/", "http://[*.]example.edu/"]
}

More detailed solution.

In command line, target your browser and add after your instruction the --use-fake-ui-for-media-stream flag, like this:

//On windows

#Normal mode
start chrome "http://localhost" --use-fake-ui-for-media-stream

#Kiosk mode (full screen)
start chrome --kiosk "http://localhost" --use-fake-ui-for-media-stream

For Linux and Mac command line instructions, see this: https://creativcoders.wordpress.com/2014/08/18/chrome-always-allow-access-to-webcam-and-microphone-over-http-webrtc/

Use command-line flag

use --use-fake-ui-for-media-stream command-line flag

example (OS X) : /Applications/Google\ Chrome.app/Contents/MacOS/Google\ Chrome http://html5-demos.appspot.com/static/getusermedia/record-user-webm.html --use-fake-ui-for-media-stream

More info here http://creativcoders.wordpress.com/2014/08/18/chrome-always-allow-access-to-webcam-and-microphone-over-http-webrtc/