Hi we used DP2-BSW Soft Imaging Soft ware for measuring spore or other particules. this software combined with Olympus BX51 in our lab. May be it can be solution for your problem
there are several image analysis systems which are created for different purposes. Each company producing microscopes have its own image analysis software.
One of several software produced by Olympus company is QuickPHOTO MICRO system. This system is basic but is sufficient for your purposes. Nikon, for example, produce more sophisticated NIS-Elements software. Each microscopy sales specialist give you more information
I dont know that my computer can use your mention software or not. Can I download this software (Olympus BX51, or Quickphoto micro system) on internet then install in my computer??
I used it for quantification of parasites, but did not measure length/width of oocysts... you probably would need to calibrate and constantly use the same camera/microscope settings. Measurement of an area is possible as far as I remember... maybe this helps?
if you can save your image files (or screen copy) and if you can calibrate the image (i.e. 1pixel = xx µm) by using the image of a know length (i.e the microscope ruler), you may open these files with the free open source software GIMP to measure the length and width of the oocyst (or any object) by using tool -> measure. Then you will be able to convert pixels into µm in an excel or libreoffice sheet.
With GIMP you can also add a mark or a number on each object you are measuring so you can make a link between images and measurement data, avoid duplicates and make valuable statistical analyses