I see a lot of cropped screenshots on support forums, when really it would be better if the poster took the screenshot of the whole window, and then just highlighted the area they are worried about with a red square (or if you are a StackOverflow user, a freehand red circle ;)). Often the answer lies outside the area the poster thinks is relevant and if one could see it immediately, it would save lots of questions and back and forth.

That said, automatically annotated screenshots would be useful, or even better: if someone invents a screengrab tool that would semantically tag all parts of the image based on the data available so its not just a plain image. I.e. screengrab a GUI window and all the text displayed in that window could be added as metadata like titlebar/button/label text and then it becomes searchable. I guess it would need an API that the developer of the app would have to explicitly implement though for most useful results like debug state information...