The photo to post as a story. The photo must be of the size 1080x1920 and must not exceed 10 MB. The photo can't be reused and can only be uploaded as a new file, so you can pass “attach://<file_attach_name>” if the photo was uploaded using multipart/form-data under <file_attach_name>. More information on Sending Files »
Type of the content, must be “photo”
Describes a photo to post as a story.