On, say, photobucket, you have link options. Click the IMG option (pic below) to copy it and then paste it into your post. If you write a sentence in your post and then paste the photobucket IMG link right below it, then your pic has a sentence right above it.
You can also attach a pic from your computer using the T4R software available when you click "go advanced" when preparing to post instead of "post quick reply". This, however, has limits and should only be used occasionally with small pics as I did in this post.