It sounds like you're wanting to use the icon to put a photo right into a post (right?), so you will need an image URL, which basically just means that the image has to be posted somewhere else on the internet (Facebook, a photo hosting website, etc). To get the image URL, go to whichever photo you want to post, right click on it, and 'copy image address'. That is what you want to post in between the
.
Is the photo you want to post already posted somewhere else online?