Identify is a useful tool from the ImageMagick basket to remember. Any time you are at the shell and want to quickly learn some information about any type of image file, try
$ identify foo.png foo.png PNG 203x463 203x463+0+0 8-bit DirectClass 9.31KB 0.000u 0:00.000
For more detailed information:
$ identify -verbose foo.png
This will literally give you all the information you can imagine about the image file.
To query for certain specific properties of an image file, see the other options that can be specified to Identify here.
Tried with: ImageMagick 8:126.96.36.199 and Ubuntu 14.04