Have you looked at photo submission requirements on-line and noticed that some places want to have IPTC info included with your photo? Wonder what IPTC stands for and what is the Photo Metadata Standard specification? The International Press Telecommunications Council (IPTC) publishes Photo Metadata Standards that are available for electronically tagging your image files with information about the image that can be very useful to you as a photographer.
These standard Metadata tags allow you to embed information into your photo: your name, Copyright and contact information as well as the caption (description) of the image and any keywords you want to apply to it. This is important so that if someone finds a copy of your image and wants to contact you about using it, they will have a method to do so. It is also the best way to make sure that your copyright information is kept with the image and, since most photographic print vendors can read this information automatically when you upload your picture, this simplifies the process of entering and editing the information available on those web sites.
Most photo editing and work-flow programs available support some parts of IPTC so you should check with your program documentation and make sure you know how to enter the information correctly and verify that it can make it though your process and convey your important data to the final product. Once you master the IPTC process, you may only need to edit your photo information once and not spend time retyping it each time you want to use your photos.
Here are some examples:

IPTC edit sample
IrfanView is a freeware program that runs on Windows platforms (also on Linux under WINE) for looking at photo image files and has a plug-in that handles IPTC entry and editing. It offers a simple interface, just fill in the fields with the information you want to store and save your changes. This program uses the original IPTC standard and its data should be readable by programs using either the original standard or the newer version that is slowly being adopted for metadata transfer.
Lightroom® is a commercial product by Adobe®
that allows photographers to process their photographs and it also allows you to enter and edit the IPTC metadata fields. As with many things in Lightroom, there is more than one way to enter your IPTC data. The best I have found so far is to use the template editor, pictured on the right. Note that with most programs only supporting the older IPTC standard, fill in both the copyright text field and the copyrighted flag so you have Copyright information regardless of what program reads your information. As always, you should verify that your necessary information is readable by your vendor because having the wrong information does not help you.
Updated March 2, 2010
If you have further examples, please feel free to send updates to me.