Gradia

Gradia helps you get your screenshots ready for sharing, whether quickly with friends or colleagues, or professionally with the entire world.

Key features:

• Add optional image and gradient backgrounds to your images
• Adjust aspect ratios and padding to fit different platforms
• Ten annotation modes, including text, arrow, and censor
• Multiple ways to import and export screenshots
• Quick upload button for image services like Imgur

Want a keyboard shortcut on GNOME?
Simply go to Settings → Keyboard → View and Customize Shortcuts → Custom Shortcuts.
Then create a shortcut that runs:

gradia --screenshot=INTERACTIVE