It can capture small entries in city directories so you don't have to save the whole page--and it adds the URL with every image.
There are lots of good screen capture utilities, and whatever works best for any particular user is the best one for that user to use. So my comments are not so much about any particular utility as they are about the notion of not saving the whole page.
I started out working more or less the way you describe - capturing the image of just the data I needed. But I have gradually changed my mind and feel like it is usually better to capture whole pages. Well, it's not so much the "whole page" that you want to capture as it is the metadata - dates, page numbers, names of publications, etc. For example, if you capture a whole newspaper page then you get the name of the newspaper, the date of publication, and the page number. Similarly with ancestry.com pages I think you are probably better off in the long run downloading whole JPG files so you get the full context of the data and most of the time you also get the metadata. With screenshots of browser screens, I think you are better off capturing the whole screen including any data that is scrolled off the screen. For example, Chrome can be used to save the screen image as a PDF, including data that is scrolled off the page.
I certainly agree that the annotation feature of your screen capture utility is a really neat feature, as is the feature to include a URL automatically. And to a certain extent, these features take care of capturing the metadata that I'm talking about. So it may be six of one and half a dozen of the other as to whether capturing whole screens and whole JPG files is really necessary. But it is something to take into consideration when devising your strategy for capturing images.
It's a little off your initial subject, but I have similarly been increasing the amount of information that I include in the file names for image files. I've gone from just the person's name in the file name (e.g., doe_john.jpg) to the person's name and the event (e.g., doe_john_obit.jpg) to the person's name, the event, and the date (e.g., doe_john_obit_1997.jpg), etc. In other words, the metadata can sometimes be almost as important as the data.