I love the windows snipping tool. Use it to "capture" your screen.
For windows, go to Start -> All Programs -> Accessories -> Snipping Tool
A great tool, and has the option for saving as png, jpg, gif. (I seem to like png lately.)
In Encore, select the flowchart; make sure the window is open so you can see what is relevant.
Open the snipping tool; drag to select the flowchart window. Save.
When making a post in the forum, you will see a "camera" icon. Click that and it will let you insert the image.