An image processing apparatus, a method, and a program for allowing cells to be quantitatively observed. A computer obtains a cell membrane image obtained by performing fluorescent observation on a cell membrane of a cell serving as a sample and a tricellular tight junction (tTJ) image obtained by performing fluorescent observation on a protein localized in a tTJ of the cell. The computer derives the size of area of a region of the cell by identifying the region of each cell from the cell membrane image, derives the size of area of the region of the protein localized in the cell from the tTJ image, and dividing the obtained size of area of the region of the protein by the size of area of the region of the cell, thus calculating an index of adhesion strength of the cells. The invention can be applied to an observation system.