What are some alternatives?
When comparing Gyazo and Greenshot, you can also consider the following products
ShareX - ShareX is a free and open source program that lets you capture or record any area of your screen...
LightShot - The fastest way to take a customizable screenshot.
Snagit - Screen Capture Software for Windows and Mac
LICEcap - A straightforward, high performance application that enables users to capture a portion of the desktop and save it to . GIF or . LCF, LICEcap is available for download as a GPL free software.
PicPick - PicPick screen capture software enable you to grab an image on your computer screen, save, print, add effects, and share.
Snipping Tool - Use Snipping Tool to capture a screen shot, or snip, of any object on your screen, and then annotate, save, or share the image