We've been using ImageJ/FIJI a lot in Biol411. We used it to measure elytron length for the beetle museum project. For our current class project (giant lit review on the effect of temperature on insect life history traits) we're going to use it to digitize figures from published papers. Here's how to get started, in case you want to do the same: 1. download the Figure Calibration plugin. 2. Open FIJI. 3. Go to Plugins --> install Plugin --> select the Figure Calibration plugin. Now, open the figure you want to digitize in FIJI. Draw a rectangle around the box of the figure. Go go to Plugins -> Figure Calibration. A box should come up that lets you input the x and y coordinates. Then use the point tool (or line, or whatever), to click on the spot you are interested in. Then hit 'measure'. Voila!
Eg - The figure below is from Laws and Joern 2012, Predator–prey interactions in a grassland food chain vary with temperature and food quality. Once you get the plug-in installed in FIJI, open up the figure, then draw a box on top of the axes, like I've done in red, below. The go to --> figure calibration, and input the axes. In this case, I'm not interested in the x, so I've just left it as is. I have inputted the y-lower, and y-upper. Then use the point tool to click on the top of the bar graph (hit Measure), as well as the error tick (hit Measure). Now you'll have your mean and error for each bar.