miniPaint - Online graphics editing tool use HTML5 technologies like Canvas, Offline support, Drag and Drop.
ImageJ - and Other Health Care
JugiPaint - JugiPaint is a painting software with diverse tools for various types of illustration work.
Fiji - Fiji: A batteries-included distribution of ImageJ.
RealWorld Paint - RealWorld Paint is an free portable image/photo/animation editor.
Image Pro - Used by researchers worldwide, Image-Pro Plus image processing software makes it easy to acquire images, count, measure and classify objects, and automate work.