doc openfig
returns a figure object, i.e. the window containing the axes. You need actual image data. With numerous assumptions on what is actually in the figure you can get this data as e.g.
hFig = openfig( ... );
hAxes = hFig.CurrentAxes;
hImage = hAxes.Children;
I = hImage.CData;
It's a very brittle way to achieve this though. image data should be stored in image files or in .mat files that you can load the actual data in from and use that directly rather than having to fish the data out of a figure.
The above assumes you have 1 axes in the figure and that the only thing in that axes is the image which you want.
