Create an IMGUR account and use it, its easy.
To upload pics to your account, just click the green "Add Images" button at the top right of the page, then drag and drop from your picture files into the box...
To post, go to your images page.
On your images page, you'll see a bunch of thumb nail pics.
Click on the pic you want to use and you get this window
Pick a size on the bottom right of the window, then click the blue BBCode COPY box, second from the bottom. Paste the code here in the forum text box.