See also this post by Allan (Dan E.)
ImageJ is a simple, free software package available for analyzing images. The download is available here.
It can be used for, among other things:
- Measuring leaf area for specific leaf area measurement from scanned images or photographs
- Assessing percent leaf disc consumption from herbivore leaf choice experiments
- Counting seeds from photographs
- A million other things
ImageJ is also amenable to batch processing. Below are protocols (written by other people!) for various applications.
Measurements of leaf area from field photographs (also generally good for scanned images): Leaf Image Protocol_NKraft
Batch Processing: Image J batch processing_NKraft
Percent leaf disc consumed from herbivore leaf choice experiment: Using ImageJ_KNurkowski