The ImageFileInput class will read a standard image file (in a common
file format, such as SGI's RGB format or JPEG format) and then its GetImage()
method will return this image the first time it is called, and NULL
thereafter. In addition, the possibility of reading several numbered files is
available, in which case it will return NULL after the last image file
is read.
The GetDimension() method will naturally return the size of the image(s) read in.