Standard for embedding time/location info into digital images?

Question

I am developing a project that involves compiling in real-time photos taken over a large area submitted (semi-)anonymously (meaning it doesn't matter who submits pictures but a minimum of info is collected), as part of a "live" massive online photo-documentary.

It is important to authenticate times and locations when and where photos were taken, as the idea is to have a "live" and "authentic" event. Photos will be edited as they come in, but we are looking for a way of authenticating them.

I am wondering what if any standard exists to embed info in digital photos (such as watermarks or meta-data) that contain location and time info, whether most camera systems nowadays implement these, and which if any is most widely used? Note that this is not a question requesting opinions about which is the best system, only insofar as to whether there is any way of authenticating the time/place info.

So:

• what standards are available, if any, for stamps with time/location
• do most cameras implement these now?
• which is most widely used
• are there systems to authenticate location/time info, if so which

Edit

The current answer has been quite useful. I have also found this link which provides a pretty useful overview on the concept of meta-data analysis, but still leaves me wondering about the details:

"Metadata analysis is one of many different types of analysis. The interpretation of results from any single analysis method may be inconclusive. It is important to validate findings with other analysis techniques and algorithms"

That's pretty open-ended, particularly when the idea is to collect and sift through lots of images in real time, ideally using some automation/programming. The current idea is then to request at minimum a timestamp and ideally location info in EXIF meta data.

Answer 1

For embedding standard metadata in images, EXIF is considered the primary standard, which provides well understood fields for time and location information.

http://en.wikipedia.org/wiki/Exchangeable_image_file_format

In addition, EXIF has a tag known as 'maker data' that allows 3rd parties to embed custom tags. This is typically where a Canon or Nikon embeds camera specific metadata, and they do not usually share the contents of their custom metadata. However, you could certainly use this area for your own needs as well, though it isn't 'standard'.

Finally, IPTC (International Press Telecommunications Council) publishes their own standard, which has more extensive metadata. This is often supported by editing and photo management software, rather than cameras.

https://iptc.org/standards/photo-metadata/

IPTC provides more fields related to location, scene subject, etc that might prove useful to you as well.

Answer 2

I recommend you follow Metadata Working Group guidelines. They build on and in some cases override the older exif and especially IPTC standards.

MWG Location Guidelines