[barrystaes]

For documentation: The best screenshot is no screenshot. Let your UI be your documentation, with UX that allows people to find and learn.

For pre-release screenshots: crude photo editing or preferably a ui wireframe tool.

For marketing: a demo login would be great, and for the few places that you demand a screenshot just take it manually with a user and content created specifically for that purpose.

For keeping up to date: if you must, have an automated job (much like CI UI test job) to take and upload screenshots whey you deploy to production.

For finding versions: have your SAAS show the version in a corner, always. I prefer a ISO8601 timestamp of the frontend build.