Error "can't be opened because it was not downloaded from the App Store"
If you are a Mac user, you may get the above error message when installing Gyazo.
In that case, go to
System Preferenceson your Mac and open
Security & Privacy.
You may see that
App Storeis selected in the above
Allow apps downloaded from:.
If the text is grayed out and you can't change your selection above, click the lock icon at the bottom left and enter your Mac login password.
When the lock icon is unlocked, change the setting to
App Store and identified developers.
Then try download and install Gyazo again.