I've worked out this still is from chapter 7 Unhappy Ending
this is how ive worked it out
These shots were taken during filming and the stunt double is in the same clothes as bella in the still and so is Jacob therefore it is from when Jacob rescues her which in the book is just after Rosalie tells Bella her story.
(WARNING POSSIBLE SPOILER) do not read on is you want surprises
It appears (if you have read the leaked script) that the scene that happens above is actually merged with the scene from the trailer when Jacob turns up at school to warn Edward but in the book he leaves and they go to class. So the still could actually be earlier in the film, depending on where they slot it it..........It is definately when Jacob "rescues" her from school.
first pic source www.facebook.com/Twilight
other pics SOURCE