afni.nimh.nih.gov

It's worth a shot. But I have found TIFF files generally don't carry the quantitative information very well. Some relative magnitude associated with a voxel may be lost particularly for color images. Gray scale images would work better. So changing the contrast or manipulating the color scale or LUT in any way might produce unexpected results. It would be even worse for JPEG images which are generally lossy compressed. Still this might work for your particular application.