File Upload Forms

To actually upload the files, you need to properly set up your form. A form that uploads files needs to have its method set to POST and its enctype set to multipart/form-data. If it’s set to GET, it won’t work at all, and if you don’t set the enctype, only the filename will be transferred.

The field itself should be an <input type=file>.

<form method=POST enctype=multipart/form-data action="{{ url_for('upload') }}">
    ...
    <input type=file name=photo>
    ...
</form>