Here is the way I do it, if I have the pictures on my hard drive
1) Go to
http://photobucket.com/ and make an account for yourself.
2) Photobucket's interface is fairly self-explanatory, just follow the instructions and upload your pictures to your account.
3) When you view your account, place your cursor over the picture, you will notice that each picture has four copyable links under it.
4) Copy the link which has "IMG" tags in brackets before and behind it. You should get something like this:
Paste this into your post and presto