I have found Flickr to be much easier, as it will automatically resize photos for you. Upload the photo to Flickr. Click the right pointing arrow to share, choose BBCode, in the box below choose your size. The only tricky part is filtering out their advertising/link coding from the actual URL. To do that:
Right click and copy the highlighted link they give you. Then paste it into notepad or even the forum textbox and weed out the junk. You want the URL that looks like "https://www.flickr.com/yadayadayadaetcetc/123456789.jpg
Delete out all the rest of the junk except that. If you are uploading an avatar, choose the 150x150 square size, do the same as above, except trim the "s" off of "https" Boards are quirky about the "s" for some reason.