ImageJ is a public domain, Java-based image processing program developed at the National Institutes of Health. ImageJ was designed with an open architecture that provides extensibility via Java plugins and recordable macros.

Image Pro is described as 'Image-Pro Plus image analysis software makes it easy to acquire images, count, measure and classify objects, and automate your work. This software offers microscope control, image capture, measurement, count/size, and macro development tools' and is an app. There are four alternatives to Image Pro for Mac, Windows and Linux. The best Image Pro alternative is ImageJ, which is both free and Open Source. Other great apps like Image Pro are Fiji, Icy Image Processing and MIPAR.
ImageJ is a public domain, Java-based image processing program developed at the National Institutes of Health. ImageJ was designed with an open architecture that provides extensibility via Java plugins and recordable macros.

Fiji is an image processing package—a "batteries-included" distribution of ImageJ, bundling a lot of plugins which facilitate scientific image analysis.

User-friendly, research-grade software to acquire, visualise and quantify 2D to 5D biological (microscopy) images

MIPAR is a revolutionary image analysis software, capable of identifying and measuring features from nearly any image one can capture.