Get a professional head shot photo taken. You can use this picture on your LinkedIn profile, your departmental web page, and other places you need a professional presence. Plus, it takes less than 5 minutes.
Graduate students and postdocs can sign up at https://iowagraduatesuccess_careers_photo_booth.youcanbook.me/ .
What to wear: The picture will have more value to you if you dress professionally. It is however just a head shot, so it isn't a problem to spruce up bit just for the photo - put on a tie or jacket for a minute. There isn't time for a whole wardrobe change, but some students have gotten two pictures, wearing a lab coat in the second one for instance.
Like all Grad Success services, the Photo Booth is FREE to all graduate students and postdocs in programs served by the Graduate College.