Images are not displayed well in a quiz.

Enter the folder name and file name used in the quiz sentence in single-byte alphanumerical characters.

Do not use full-width in the file name, use only alphanumerical characters. If you fill in other than half-width alphanumerical characters, the image will not be displayed.

Also, make sure that there is no whitespace in the [[ ]].
e.g.) If you write [[image/tree.jpg]] instead of  [[ＩＭＡＧＥ/ＴＲＥＥ.jpg]], the image will be displayed.

You can read more about it in the link below.