Wear a solid-colored shirt like a common button up, polo shirt or T-shirt, don’t wear white shirt or blouse. Do not wear your work uniform.  To make an even better photo pick a shirt color that flatters your skin tone. If you have pale skin, try navy or dark green. If your skin has gold tones, choose an orange or deep brown shirt, while people with olive or dark skin will look good in vibrant shades of red or blue.  I suggest you dress somewhat formally and conservatively, because the people who examine your passport tend to be pretty conservative. There are countries where dress that is too casual or revealing can get you into trouble, so make sure the passport photo is somewhat conservative – because you’ll be using it for the next 10 years!