Possible Clues:

• Ask, as questions
• Sit for a shooting
• Act
• Prepare to be painted, say
• Stance before a selfie
• Word that forms a new word when appended to the end of the answer to 18-, 27-, 47- or 58-Across
• Tree or downward dog
• Sit for a portraitist
• It may be struck for the camera
• Act (as)