He spent a long time with this and couldn't think of anything better than to upload a photo to a group album, and from there to attach to the wall. But now literally on the knee came up with an algorithm that in theory could work.
If do you want to download photos methods photos.getWallUploadServer
as you do, the photo album off the wall (vk.com/album-12345
_00 - bold to change the ID of your community), a downloaded photo can still be added. And she is there on behalf of the community. Assume that in this case is a method of photos.get
to ID latest photos and attach it to the post.