I like to use the program ImageJ for analyses like this. You do need some sort of scale to establish area or distance, but this can be done with an object of known length that appears in the image. I have done this for pictures in which there was not a true scale (e.g., a ruler) in the image. You just need something that you are confident of the length. In my case, I used eggs that appeared in the image since I had good data on average egg diameter. You can then scale the number of pixels to a known length and, then, calculate area of the entire photo or sections of the photo.
ImageJ is a free download here: http://rsbweb.nih.gov/ij/ Geoffrey B. Steinhart Assistant Professor and Co-director of the Aquatic Research Lab President-Elect, Michigan Chapter of the American Fisheries Society Lake Superior State University School of Biological Sciences 650 W. Easterday Avenue Sault Ste. Marie, MI 49783 phone: 906.635.2093 web: http://www.lssu.edu/faculty/gsteinhart On Jun 22, 2010, at 12:00 AM, ECOLOG-L automatic digest system wrote: > Date: Mon, 21 Jun 2010 15:31:10 +0100 > From: Beth Strain <[email protected]> > Subject: Photo analysis question > > Dear Ecology List Server > I have recently been given a set of photos which I would like to > convert into densities of species. The photos were taken haphardly but > do not contain a quadrat or transect. The photos cover a 1-2 m area. I > wanted to ask if anyone had any suggestions about how to calculate the > area of the photo. > Thanks for your help > Beth Strain.
