Free APIs, online services to generate screenshots of web pages

I've graded the answers to this StackOverflow question about APIs & online services to generate screenshots of web pages based on whether the service can be used directly without any API key or require a key:

No key required:

• immediatenet.com
• kwout API (generating screenshots is not the primary intent of kwout so it doesn't directly give you an image to save)

Requires (free) API access key:

• URL2PNG
• Browshot API
• GrabzIt
• thumbalizr API (Simple syntax to use the API: http://api.thumbalizr.com/?url=http://mvark.blogspot.in&width=250)
• ConvertAPI (Free 500 one-time credits)

There are also online tools can generate screenshots of websites:

• Browsershots.org
• WebShots Pro
• ShrinkTheWeb
• Amit Agarwal's Screen Capture tool
• GrabzIt