The problem is with the image field and would not be a problem with a text field. the_field() echos the field value, in this case an array that cannot be converted to these. If you return an array for an image field then you must read the elements of the array and create the output yourself as needed. This is covered in the documentation. ACF will not format the html for the image for you when the field is set to return an array. You will find that this is the case with most of the more advanced field types.
