Plot hole: The pictures used in the newspaper article regarding the fire are obviously taken after Ponyboy and Johnny ran away since Pony's hair is blond and Johnny's is short (their hair was cut and dyed after they ran, ruling out the photos being old school photos), yet Johnny's face is free of burns. This would mean the pictures were taken while they were hiding in the church, which would be impossible.
Deliberate mistake: During the rumble scene it's raining and everyone gets wet and muddy. Right before the Socs surrender, we see one of the Socs whose clothes are completely dry and clean. He's wearing a light blue shirt.
Suggested correction: That was to show he was the toughest of the Socs' group and that no one took him down. This was not part of the book but a choice by the director.
Stupidity: Johnny bleaches and cuts Ponyboy's hair and cuts and washes his own, thinking that would make them not fit the pictures of them. They look the same just with blonde hair and not greasy hair.
Suggested correction: I think you are right to a certain extent, but not necessarily when things are put in perspective. For example, they were "Greasers" and a certain image was attached to this status. Something like washing their hair would make them less noticeable among "Soc's" and other non-Greaser statuses. Anyone looking for them would not automatically assume they washed their hair or had the time to get hair cuts and bleaching while "on the lam." If an APB went out, it would contain their usual appearances.
Suggested correction: They could just be an old photo. Taken a year or two back, plenty of time for them to look roughly the same but have their hair change wildly. Could have dyed his hair and then stopped or cut the hair and then let it grow.
Ponyboy's reaction to his blonde hair after Johnny dyes it is one of disgust; he did not dye it blonde ever before. Plus, it wouldn't make sense for him to dye it blonde again if he was trying to disguise himself.