The desktop is captured instead of the desired location
After updating to new Mac OS, the background wallpaper may be captured instead of the desired webpage or app window.
The solution is simple.
Follow these steps to fix the issue
1. Open System Preferences
2. Select "Image Capture" from "Security & Privacy"
3. Check Gyazo, Gyazo GIF
After changing the settings, start Gyazo again and you should be able to capture normally.
You can read more about privacy on this page: Is Gyazo safe?