Measurable area, accuracy, and ranges of displacement, strain and rotation of the CASI are estimated. The measurable area for a given video camera is proportional to the area of each individual speckle. The displacement uncertainty is proportional to speckle size. The measurable displacement ranges from a few percent of speckle size to several centimeters. Strain and rotation up to 3 ~ 5% can be detected. Experimental results from CASI on crack opening displacement (COD) and normal strain distribution ahead of a crack tip of an aluminum specimen under mode I loading are presented.