Comment by oefrha

Tried a standard input tag with the proper accept attribute

  <input type="file" accept="image/jpeg,image/png" />

Selected a HEIC file from Photos in Safari, the selected image was automatically converted to JPEG.

Ten bucks says College Board programmer(s) failed to do the most basic and standard filtering.

Edit: Like a sibling comment said, the accept attribute actually isn't necessary; even PNG images (e.g. screenshots) from Photos are converted to JPEG automatically. This is true on both macOS and iOS Safari (latest). To be clear, on macOS you need to select from Photos instead of the filesystem for this to take effect.

In case anyone's interested, source code you can use to test for yourself (a Flask app):

app.py:

  import flask
  
  
  app = flask.Flask(__name__)
  
  
  @app.route("/", methods=["GET", "POST"])
  def index():
      if flask.request.method == "POST":
          image = flask.request.files["image"]
          return f"uploaded {image.filename!r} ({image.mimetype})"
      return flask.render_template("index.html")

templates/index.html:

  <html>
    <head>
      <meta charset="utf-8" />
      <meta name="viewport" content="width=device-width, initial-scale=1" />
    </head>
    <body>
      <form method="post" enctype="multipart/form-data">
        <input name="image" type="file" required />
        <input type="submit" />
      </form>
    </body>
  </html>