The simplest explanation
is that your memory is faulty - the "message" about the ripped trousers only appeared when your mother joined the 'seance', and she created it herself using the ideomotor effect (which is how the ouija board works). Memory's a very deceptive thing, and although you might be convinced that the 'message' had appeared before she joined you, it almost certainly didn't.
(TheImmortalJenkins, Sun 16 Sep 2012, 1:13, 1 reply)

Yeah
Obviously I wasn't there, but this seems likely. There's also the possibility that she'd actually mentioned the photo to one of the other people at the table, but due to forgetfulness, politeness, or a simple love of drama they'd played along with it - consciously or not.
( Zoroastermouse thinks therefore he am, Sun 16 Sep 2012, 3:28, closed)

I'd already said
"Ripped his trousers" appeared before my mother joined. There's four people who all remember it the same. This actually happened, I was there.

Be a skep if you like, one day, maybe you'll realise there's something more than this 'life' thing we all think is so important.
( Black Moon Not cracked, I'm all up to be., Sun 16 Sep 2012, 10:49, closed)

Woah, you're not under attack you know...
...but you asked the question about "how could this be explained" and I provided a possible answer.

Step back from this, and think about the whole concept of "talking to the dead" logically, and in an evidence-based way.

If there was any sure-fire method of getting messages from "beyond the grave" then we would really know about it by now. But like all "supernatural" phenomena, there isn't a single shred of **evidence** to suggest that this is fact, repeatable in scientifically controlled circumstances. Have a look at the Randi Foundation - which has offered a prize of a $1m for some decades now if any "supernatural" phenomena can be replicated in a controlled, observed environment.

The prize remains unclaimed. Fact is, there is nothing "supernatural" that can't be explained. We all have "weird" experiences in our lives, which can basically be logically explained. However nothing can be "made" to happen under controlled conditions, and nothing ever has.
(TheImmortalJenkins, Sun 16 Sep 2012, 12:30, closed)

I know.
I see if from your side of the table, I really do, but I can't deny what I saw that night.
( Black Moon Not cracked, I'm all up to be., Sun 16 Sep 2012, 20:27, closed)