Here is a version that is more "tamper-proof"...when a user posts a dice roll, the text "Legitimate Dice Roll" will appear above the roll (you can change this text by editing the phrase "markfl_diceroll_legittext").
If a user tries to cheat and construct their own dice roll by entering the appropriate image/table BBCodes with that text above it, the text will be removed. If the post is edited, that text will also be removed.