Fn+PrtScrn to copy image
open photo editor
Ctrl+V to paste image
save image and then post like you would any other time. ie, hosting them here or on photobucket, etc. offsite hosting will allow for a larger image
There is a key labeled "Fn" on your keyboard. You hold it down and then while it's depressed, PrntScrn. Actually, you might not even need to hit Fn, as is the case on my laptop. I just hit PrntScrn.
Being able to do a screenshot can be a very handy tool.