When I bought a Mac Mini with Mac OS X, I could show image dimensions in the Get Info dialog.
After that, I installed some mobile application development software and later I noticed, Get Info was not showing the image dimensions anymore. I need to check the dimensions of those images to include artwork in my project. Now, I reinstalled my Mac OS X and it's working fine – it is showing the dimensions:
Before that, 516x314 was missing. Why did that happen? How can I prevent it from happening again?