Photos cannot be directly inserted/uploaded to posts and comments here.
To show everyone a photo, you must first upload/host your photo on a third-party site, such as Photobucket, Flickr, Facebook, etc.
Once your photo is uploaded to the third-party site, copy the link to your photo (URL from the address bar, "share" link, etc.) there and paste the link into your post/comment here, just like any other URL or web address.
Readers will then be able to click the link in your post to see your photo hosted on the third-party site.
See this Lure Making topic for an example: viewtopic.php?f=7&t=12801