Sometimes I have a picture which I don't know, or which I have taken a long time ago. So how do you identify unknown stuff on your image?
For example I saw this picture, and what is the best approach to identify the hill on it?
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I have had some success posting pictures on Flickr asking for help identifying what it is, tagging with anything relevant possible.
Try Google Goggles if your phone can do it. You take a picture and Google looks up what it is. You mileage may vary but it works for reasonably well known location even with not so direct framing.
You could try using TinEye Reverse Image Search to see if there are some similar pictures, perhaps those have some description nearby.
Find out the capture date. Then check on shots you took before and after this one. Also be sure to look into your calendar/diary (if you have one) to see where you were at that time.
That's the only way I can think of.
If the photo was geotagged, then at least you can find out where it was taken. That might be enough to help you identify the subject. (In this case, it almost certainly would, as it's a landscape shot).
Some cameras have GPS/geotagging built-in. Some can do it with an add-on module. If you have synchronized clocks and a standalone GPS, you can get software to match up your photos with your track, and apply geotags in post-production.