The link is http://epx.com.br/lesvos.
Lesvos is my newest toy, based on HTML5 Canvas. The basic idea is that you often know the size of something on the picture. For example, most people know his/her own height. So you give this "hint" to the software, and then you can estimate size on other things.
The unit of measure does not matter. You just double-click the red ruler, which is the hint, and enter the value in whatever unit you like. All other measures (the green rulers) will be expressed in the same unit.
For now, it is a 2D-only tool, so only objects on the same plane can be measured. I plan to add perspective input in some future version. *That* is going to be challenging and fun to do.
The image is not transmitted to the server. All manipulation happens at browser side. Because of this, I had to use the new HTML5 File API. This means that Lesvos currently works only on Chrome and Firefox (tested on version 3.6). Safari 6 will support this API and Lesvos probably works unmodified on it.
Coding the rulers' manipulation was quite complicated and boring. I am seriously considering using a SVG layer to handle them, keeping the canvas beneath just to paint the unsaturated version of the picture. Need to play this before thinking about adding perspective manipulation.
The name Lesvos is inspired on the mythical "Ruler of Lesbos" which has the power to measure anything, including abstract things like justice and love. It is a common methaphor for legal equity (or better said, the impossibility of perfect equity).
By the way, "Lesvos" and "Lesbos" are equivalent names for the same Greek island. I used the less-common spelling because Google AdSense was refusing to work with the other form. The page would possibly be filtered out by search engines, too. Sick (and ignorant!) conservatism.
(But I must admit that the law professor managed to wake us up all at once when he mentioned the Ruler in class :)