If you want to use a screenshot of software for an openly licensed work, as a general rule, check the terms of a website as they may spell out the rules of how to use screenshots of their products. Many companies are ok with using screenshots of their software or products for training. There are many “how to” websites that use screenshots as there is a financial incentive for companies to have training material created for them by others. (The more people who learn to use their product, the better).

If the software is open source or released under a free software license, it is usually fine to use screenshots.

Microsoft spells out how you can use screenshots of their products as follows:

• You may not use screen shots of Microsoft product boot-up screens, opening screens, “splash screens,” or screens from beta release products or other products that have not been commercially released.
• You may use other screen shots in advertising, in documentation (including educational brochures), in tutorial books, in videos, or on Web sites, provided that, in addition to the requirements above, you:
  • Do not alter the screen shot except to resize it.
  • Do not use portions of screen shots.
  • Do not include screen shots in your product user interface.
  • Do not use screen shots that contain third-party content.
  • Do not use screen shots that contain an image of an identifiable individual.

Google allows use of screenshots of their products.

Others, however, such as Yahoo, requires that you to ask permission.

Bottom line: check the website for terms of use.