As has been said, you can't
directly include an image in a post here. You need to upload it to somewhere on the web and them post a link to it here.
The most popular site for hosting such pictures is Tinypic:
http://tinypic.com/
(If you need detailed instructions please refer to my post here:
http://www.theanswerbank.co.uk/Animals-and-Nature/Question1426455.html )
However I find this site faster:
http://www.hostingpics.net/
Click the first 'Browse' button.
Navigate to the location of your file and double-click on it.
Click 'Envoyer'
When you see a small version of your picture, click on it.
Then click again on the resulting image.
Copy the URL of that page and paste it into an AB post.
Easy peasy!
Here's the same pic hosted on each of the two sites:
http://tinypic.com/view.php?pic=11lmzxz&s=8
and
https://img15.hostingpics.net/pics/46089711lmzxz.jpg
All image-hosting websites accept the .jpg format. .gif, .bmp and .png are usually supported as well.