It would seem to me that after the Krausen it may be less likely than during. Reason being many people siphon to a second fermenter which not only is an open container no matter how well you transfer you are adding oxygen. Not denying what you said just trying to wrap my head around the process.
When you add things, you don't dawdle. Open lid, add, close lid. Leave it open too long and yes, air will enter and you may get an infection.
Opening the LBK to take pictures is about the dumbest thing a new brewer can do, unfortunately new brewers often do it because they don't know better.