I have El Capitan and can not install a DMG file I get an error message that says:


  Warning. The following disk images couldn't be opened.
  Image Reason SurveillanceClient.dmg invalid checksum


Does anyone have ideas on how to install this file?
In this YouTube video, they teach you how to fix this. Anyway, after El Capitan, Disk Utility has been completely changed, so now, in order to disable the checksum verification, you can just open a Terminal window and type:

defaults write com.apple.frameworks.diskimages skip-verify -bool true


Then open again your .dmg. Now it should work.