You store text in a single line text or long text field. You cannot store an image in either of these fields.
You store an image as an attachment in an attachment field. You cannot directly store text in an attachment field. (Technically, you could store text in a text file and attach the text file, but that doesn’t sound like what you want.)
If your image is hosted on the web, you could also store the image in a URL field.
One approach is to store a text question in a single line text field, and store the image in an attachment field, and then have whatever code is accessing the API sort out which one to use.
If this answers your question, please mark this post as the solution. Otherwise, could you please give a bit more details and a screen capture?