The "media process" gets triggered by different applications. Some of them you already encountered: Camera and Download. Basically apps which add new media (or manipulate existing ones). They are signaling the media scanner that there are changes to process (so the media database gets updated). As the media scanner is, simply spoken, just a "system process", you don't see a related app.
Auto-Killing would not be very helpful in this case (for the described reasons, media scanner must do its job or e.g. the gallery wouldn't find your fresh shot pics). It rather might be that some app requests its services much to frequently (that was the issue in another case I encountered recently, but I don't remember the app causing it). So you would need to find the culprit causing that (not killing the obedient servant): Go through all the apps you've installed and check which one might deal with media (if the problem just started recently, it's even easier as you can concentrate on those recently installed/updated). See if you can temporarily disable/remove them, and if the problem is gone with that. If so, re-enable them slowly one-by-one until the problem re-appears – which is when you just re-enabled the culprit which thus is identified. That's the app you either need to find a replacement for, or have the dev fixing the issue.