Several possibilities for you to open one or more images. The first solution is to click the Open tab. The second is to click on the File menu and then click Open. The last simpler and quicker to use, you are permitted by using the shortcut CTRL + O. "
A dialog box offers you then. If your images are different in the same folder, you can open several at once by pressing and holding down the "Ctrl". You can put several images of different sizes in your image list, but for launching a calculation does not lose the idea that this can be done only on two frames of equal size. Click Open, then you will get a screen corresponding to the next image.
Only when two images added to your list, that tab to launch a calculation will be made available.
Supported formats to open are: Text, JPEG, JPG, JPE, JFIF, TIFF, TIF, PNG, GIF, BMP