[deanhills]

Because either someone else or you have changed the image size in camera. All digital cameras have at least 3 image sizes depending on resolution. Now I don't know much but I know the max resolution size it 4,608 x 3,456 pixels in your camera, Canon A2400. Now its on smallest image size, im sure. Check the camera settings you can change it from there.

Thanks @xdude.  I feel kind'a foolish as last night spent some time figuring out the problem.  I was Googling it, then downloaded the software that came with the camera - which in the end was useless as it was just a super slow version of the one that came with Windows 7 and limited to viewing photos - nothing to do with the functions of the camera.  I also downloaded the Manual and followed the steps, searching for the resolution change option in the menu, and I couldn't find the same option in my menu - that now really puzzled me.  So I did that thing one sometimes does at the end of a frustrating "learning curve".  I gave up.  Relaxed.  Took the camera, pressed the Function key - and all of a sudden saw other options in addition to the menu that came up spontaneously on the camera screen - like S for small (which is what mine was on), L for the maximum resolution, and then M1, M2 etc.  The options came as parallel to the menu options and not part of the menu options.  All I had to do is use the cursor buttons to move to L for the largest 16 mega pixels and it was done.  Too easy!

So I guess discovering how easy it is - that is probably the reason how the L got changed to S by accident.  I must have touched something that changed it at some or other stage.  I notice that with the latest Manual that that function isn't where mine is any longer.  They've moved it to the menu so one has to move through the menu options for making the resolution change.  I guess they must have figured out it's too easy to change the resolution - people must have complained or something - who knows.

Those 16 mega pixels make a HUGE difference to the photos.  Am glad I have them back again as enjoyed my photo session yesterday.  Just sorry the photos look flat and almost grainy because of the low resolution.  Next week when the weather is good again I'll take the exact same photos and compare.

BTW here are the details of my camera.  I really love this camera.  Was very interesting as two Saturdays ago when I went for a passport photo shoot at a professional studio, the guy used the latest model of this camera.  I was a bit dubious to start, but this guy knew his stuff with it.   
https://www.usa.canon.com/internet/porta...t-a2400-is