PIXEL

picture resolution :

this is the number of pixels that make up an image it normally gives you the width and height of the image for example the image below is 1366 x 768 or you can say its 1.5 mega pixels.

image resolution

this is the quality of the picture that you if you have a really bad pix elated picture then it will have poor image resolution. for example this picture would have a bad image resolution because its really pix eated.

intensity 

this is equivalent to gray scale of a pixel