After you resize your photos and upload your pictures to your gallery (or image hosting site), you right click on the actual picture (not the thumbnail of it), and then click Properties.

Next to Address it says something that starts with http and ends with jpg. You may not be able to see all of it on one line, but you should be able to highlight it from beginning to end and then right-click on it and click Copy.

Then go to your forum post (you can have these open in two windows to make it easy) and right click in the big box and click Paste. You should then see the same thing from the address field that started with http. If you will highlight it then click on the button that says IMG it should put tags that says [img ] before and [/img ] after it (without the spaces inside the brackets) and you should see your picture when you save the post.