Hosting pics from an external site is fine, but I actually recommend to upload them as attachments right in your post, especially if they're of significant 'importance' and you want other members/readers to be able to view them for years to come. A lot of times, people who use external hosting sites to link to their images will either delete the images sometime down the road, or will let their account close/expire. Then we're left with a broken image (red X) in the forum. I can't tell you how many times I've personally searched topics on forums hoping to find a specific picture, only to find that the image was broken.. and it happens more often in older threads. When uploaded directly to the forum, they'll be here virtually forever.
What I like to do is this.. upload (attach) the image when making your post, and click the submit button. Then when your post is present, click the thumbnail of your image to enlarge it. Then, right-click and copy the image URL.
Click the 'edit' button in your post, and paste the image URL (right-click, paste) in the message field sandwiched between IMG tags. Then you can type in your captions, or whatever, under or over that. Then click 'save'.
Now your image will be embedded full size in your post.
