So the Windows snip tool makes this really easy. Here's some steps that should work, and give you a quick way to clip stuff in the future:
1. Open up the photo so you're viewing it (doesn't matter what format it is) - can be on google or a forum, whatever.
2. On keyboard, hit WindowsKey+Shift+S
3. Your screen will darken and a toolbar will pop-up at the top, and your cursor will change to a crosshair. Left click and drag that crosshair to form a box around the image you want (start top-left and drag to bottom-right). When you release the button, the image will automatically be copied to your clipboard.
4. Open up this forum reply box, type in whatever you want, and then "Control+V" to paste the clipped image right into your message.
5. Click "Post Reply"
Here is an example:
Edit: Once you get used to this, it makes clipping images for texts/posts really quick and easy - and you avoid having to do the "save as" dance, throwing it on your desktop, then naming it something you forget about for 6 months when you're cleaning stuff out of your folders.