Tool to quickly hide/blur/redact text in screenshot?

I’ve captured a screenshot and I want to share it (on Stack Overflow, actually), but I need to blur/hide out a couple words in the screenshot. Is there a tool to quickly do this?

Skitch can do this quickly. See?

Just click the blur button in the side bar and draw over your image to obscure things.

Please note that this app saves files to Evernote by default which can be a problem for sensitive content. You may want to disable it by not signing into your Evernote account or by making the following setting changes:

• Set Sync -> Save New Skitch Notes to Evernote to Manual
• Uncheck Sharing -> Automatically Share and Copy Link after creating new Skitch Notes

You can use Preview in two ways:

• Use the Annotation tool to draw a filled rectangle over the area you want to hide. You can select the fill color.

• Use the Selection tool to select the area you want to hide and then cut it. The area will be replaced by a gray area (or whatever color is set as window background in Preferences/General).