This is what the Election Commission says on the Code of Conduct.

"On the day of the poll, no person who has been assessed to be having a
security threat and therefore given official security shall enter the vicinity
of a polling station premise (within 100 meters) with his security personnel.
Further, on the day of the poll no such person shall move around in a
constituency with his security personnel. If the person provided with
official security happens to be a voter also, then he or she shall restrict his
/ her movement - accompanied by security personnel, to voting only."

The picture tweeted by AAP shows Rahul Gandhi enter a poll booth in Amethi. The AAP has also filed a complaint with the EC saying Rahul was travelling around his constituency in a convoy.