The extension that I have been using is called Webpage Screenshot. This lets you capture a screenshot and edit it in the browser, including cropping. Once edited you can then share the image. This presents convenient links for emailing, sharing on facebook or twitter among others. It also the simplest way I have found to save the image on a Chromebook for subsequent uploading to Blogger.
Here's the steps once you have Webpage Screenshot installed
- click the Webpage Screenshot camera icon
- select Visible screenshot
- click the crop icon on the toolbar
- click and drag from the top-left to the lower-right of the area to crop
- click Share
- click the URL that appears above the various social sharing links
- right click on the cropped image in the page and save image as...
There is a Save button next to the Share button, however, it seems to require another extension to be installed. Using the steps above allows the image to be saved without that plugin.