kanan, its a bit of a long process but I do it all the time. I take 'em with my iphone, then I email the photo to myself. THen I check my mail on my computer, and save the photo to my hard drive.
Then I go to a photo uploader like http://imageshack.us
and upload the photo to that website. Once it's done, the site will list a "direct link to image" that you can copy and paste. If you click "Go Advanced" at the bottom of the forum where you type your reply on fatsecret, you'll get more options for the post.
One of them is a symbol of a photo of a mountain, which means you can insert a picture.
Click that, and it'll insert image tags in your post, which look like this:
Paste the direct link you got from imageshack in between the tags, so it looks like this:
After you do that, you can preview your post and see if it worked. Hope I explained that okay!