Quite a lot. In "Antiques Road Show" terminology, everything is condition, condition, condition. The straight edges at left and top are normal - natural from the corner of the sheet and detract some from the value most collectors would give. It appears this is an unsigned stamp that was soaked from a license - where the license (and stamp) was folded to fit into a wallet - so while not signed, I'll bet it lacks full gum. Yeah the crease detracts, so does the damage to the lower right side perforations and the adhesion to the upper wing, which might be treatable. Serious duck stamp collectors would classify this as a space filler at about 10% catalog.