"JShot is a free and multiplatform screen capture and uploader application which allows you to capture and annotate a part of your screen and share it via the Internet in one step."And as luck would have it, one of the upload options is for Google's Picasaweb that helps provide images for Blogger.
JShot is a usefully featured screen capture program. It is fast in screen, area or region capture. JShot has an optional toolbar dock that lets you quickly take the screenshot you want. There are several easy to select and use annotation tools. The tools include circles, ovals, squares, rectangles, arrows or text. I like the transparency and highlight options for those tools. Arrows and text input pivot and rotate with little effort. Text input font is easy to modify.
JShot will also open arbitrary image files for annotation beyond just the screenshot image taken. Nice additional features include the mentioned Picasaweb single click upload as well as FTP or Dropbox to name just a couple. You can even free-hand draw on your screen prior to screen capture (yes that is close to my normal handwriting scribble).
JShot also includes an extendable plugin capability for those needing something more. Did I mention the Java Web Start option?
There are just a couple of minor issues from my usage attempts. First, large images can not be scaled to fit on the screen. Also, the shapes can not be rotated (not that you rotate a circle). They move on an vertical or horizontal axis only. The "File" -> "Open" dialog does not remember last settings (for stuff like this, the date sort is more often what I want). I would also like to see the auto-number name incrementing that other screen capture utilities have like ksnapshot. Another only slightly annoyance is the "File" -> "Exit" produces a "All unsaved data will be lost" message even if you *just* saved. Fairly nit-picky issues overall. None outweigh the very useful capability.
I have not been much of a java app fan, but JShot is a very well done utility that will remain in my Linux geek toolbox. Hope you enjoy this utility as much as I have. And just to be clear, JShot screen capture and annotator works for Mac, Windows and Linux.