There probably is, but I can't find it
If you're posting on a computer or laptop there's a little icon of a mountain, to the right of the smiley button above the text box that you're typing into. Click on this and you will get a box with a field for you to insert an image url. This assumes that you have the image hosted on a website (Photobucket, Flickr or some such) somewhere. If it's on your PC I'm not sure you can browse and insert it. If you're using the phone app and the pic is on your phone, tap on the mountain icon (left-most of the icons below the text field) and it will give you a choice of sources to pick from on your phone, including your photos. Alternatively, if the pic is online, put the url between {IMG} and {/IMG}, but using square brackets - [ ] rather than curly ones - { }
Hope this makes sense, of a sort
(Edit: I'm tagging
@Giverny, who my be able to help better than me
)