On my work computer, I fight a constant struggle against the standard apps in OSX that launch at the most inopportune times. The greatest offenders are iTunes, that hijack the media buttons (back, play/pause and forward) to launch itself and Photos, that likes to start up every time I hook in a new iOS device.

However, there is actually a simple, built-in way that will prevent this from ever happening. If you go into the /Applications/ folder and bring up the info sheet for the Application in question and select “No Access” for the groups everyone and system. You must first click the little lock in the lower right and enter your admin password to allow you to make changes. This will prevent those apps from ever launching again, they will only briefly appear in the Dock when prompted.

The group everyone has been assigned no access in OSX file info sheet, screenshot from OSX
No access for iTunes & Photos makes me a more productive person.

The only drawback of this method is that you can no longer use those apps. However, for me that has a dedicated work machine. This is a very reasonable sacrifice. I have no desire to open Photos on it and preventing me from doing so is only a benefit in my eyes.