I am sorry for your loss.
I would not have wanted similar photos posted on Facebook myself, but your brother felt differently, and I am certain he meant no disrespect to your mother, but felt he was honouring her. She was after all his mother too. Presumably, he did not realise that this would hurt you.
Try not to upset yourself over this. He is your brother, so try not to take it out on him that you and he think differently about this.
I was asked by a younger relation to take photo of my husband before his coffin was closed, as she was not able to attend his funeral. I dutifully asked the undertaker if he would be kind enough to take the photo, which he did and then the young woman turned round and said she had reconsidered and did not want the photo.
Frankly, I would rather not have had it taken, or have had to see it, as the undertaker e-mailed it to me. But there it is.
Immediately after the funeral everything hurts. As time passes, I hope you will find, as I did, that this no longer rankles.