Google Chart API
“The Google Chart API returns a PNG-format image in response to a URL. Several types of image can be generated: line, bar, and pie charts for example. For each image type you can specify attributes such as size, colors, and labels.”
“You can include a Chart API image in a webpage by embedding a URL within an tag. When the webpage is displayed in a browser the Chart API renders the image within the page.”
“This document describes the required format of Chart API URLs and the available parameters.”