How do I post a photo?
The New Post page has a button labelled "Add Photos" that you can click to add photos when you are submitting new posts.
If you have problems adding a photo using the New post page, most groups allow links to photos in the details section of your post. So you can use a site like Flickr, Dropbox or Google Photos to upload your photos and then just include a link to those photos in your post details.
If your trying to add photos to an existing post, you can edit your post to add photos to it.