Imagemagick identify is pretty handy utility to get information about an image. You need to have imagemagick installed on your Mac or Linux for the purpose of this tutorial. Here are some scenarios to get image information:
Print image size (pixels) and PPI
Image size (pixels)
$ identify -format "Pixel Size: %w x %h\n" img1.png Pixel Size: 487 x 259
Image PPI (pixels per inch)
$ identify -format "PPI: %x x %y\n" img1.png PPI:72 x 72
Note: to find actual image size, you can divide pixel width by width PPI.
Print image width and height in inches
Width in inches
$ identify -format "%w/%x\n" img1.png | bc -l 6.76388888888888888888
Height in inches
$ identify -format "%h/%y\n" img1.png | bc -l 3.59722222222222222222
