I gave you a drag and drop method to save you some typing, weird as it may seem, it works. Impavidus has given the full command, substitute the correct path. The copying to a text file was for easy manual comparison with the source md5, that's all.
Edit: to clarify after re-reading post 18. When you download an iso from the net also source and copy the md5 checksum published with it. This is what you compare to the one for the downloaded file you checked in terminal.
Here is a list of md5 hashes for Ubuntu,
Your installers hash will be in there for comparison.