The correct passive form of the given sentence is:

☀ Let the picture be seen by him.

Let's break down the options:

1. Let the picture be seen by him. (Correct) This sentence correctly uses the passive voice and maintains the original meaning, indicating that someone is allowing or permitting the picture to be seen by "him."

2. The picture is seen by him. (Incorrect) While this sentence is in the passive voice, it lacks the imperative construction "Let," which changes the meaning. The original sentence is an imperative sentence that uses "Let" to make a request or permission.

3. Let him the picture be seen. (Incorrect) This sentence is not in the correct grammatical structure for the passive voice. The correct form is "Let the picture be seen by him."

4. The picture is seen by him. (Incorrect) This sentence is in the passive voice but does not include the "Let" construction from the original sentence, which changes the meaning. The original sentence is an imperative, requesting or permitting someone to see the picture.