We are able to to retrieve the properties of an image file such as resolution, number of pixels and so on, using a 3rd party free application, such as ImageMagick.

Once the installation* has been performed, simply use the "Run DOS Command" Action with the following configuration:

The output will be stored into the variable %CommandOutput%, whose type will be a Text Value and can be easily manipulated with the "Text Actions". 

*Note: During the installation, make sure to check the following options: