This is no longer maintained. Who knows maybe I'll motivate myself enough and build the web-based SteaScree 2 at some point!
SteaScree is a simple cross-platform open-source utility app, which makes screenshots, taken without the use of Steam's in-game overlay, uploadable to the Steam Cloud. You just pick pics, a game and SteaScree will do the rest.
Latest installers for all platforms are always available at https://steascree.download.
Join official Steam group for the latest announcements and discussion: http://steamcommunity.com/groups/steascree.
Developer's note: I am sorry I was unable to motivate myself to improve this app in recent years. The thing is, I don't feel like learning Qt and the build process for different platforms is a bit cumbersome. That's why I don't feel like Qt is a way to go, well... not anymore. I am thinking about rewriting SteaScree for a browser, that is in JavaScript using File System Access API, but that'll obviously take time.