Here's what you do.
First you need to find the image you want to post. It has to be on the net. Not on your computer. So if you have pictures on your home computer, you will need to upload them to the net. You can use
www.photobucket.com (just one of many). Now that you have a photo on the net. Click on whatever you need to do to bring that picture up. Then right click on the photo and then left click on "copy image location"
Now back to the message that you want to post it in. Below the window you are typing in you will see some black buttons below the view smilies. Click on the image button. A window pops up. Right click in here and left click paste.
Then click OK. That's it. Try it and see what happens.