Preventing users to upload BMP, TIFF etc. images to ImageField in Plone

The users do it because they can.

However, image auto-resize etc. breaks down.

This make me a sad boy.

How to limit image uploads to GIF, PNG and JPEG sitewide?

For Archetypes
For Dexterity

Solution

i ran into similar problems these days and worked around them like that:

add a custom widget that adds an accept attribute to the file input
set field.swallowResizeExceptions = True so users at least don't get a site-error when uploading an unsopported image type
state mimetypes that work in description

The field definition looks like this:

atapi.ImageField('image1',
    swallowResizeExceptions = True,
    widget = atapi.ImageWidget(
        label = _(u"Image 1"),
        description = _(u"Image used in listings. (JPEG, PNG and GIF are supported)"),
        show_content_type = False,
        accept = 'image/*',
        macro = 'mywidgets/myimage',
        ),
    ),

note that accept="image/jpeg,image/gif"was ignored by firefox11 although it sould be supported according to http://www.w3schools.com/tags/att_input_accept.asp

mywidgets/myimage is a customized version of archetypes/skins/widgets/image.pt that uses a customized version of archetypes/skins/widgets/file.pt

<metal:define define-macro="edit">
...
   <metal metal:use-macro="here/mywidgets/myfile/macros/file_upload"/>
...

and mywidgets/myfile.pt simply defines this macro:

<metal:define define-macro="file_upload"
       tal:define="unit accessor;
                   size unit/get_size | python:unit and len(unit) or 0;">
    <input type="file"
           size="30"
           tal:attributes="name string:${fieldName}_file;
                           id string:${fieldName}_file;
                           accept widget/accept|nothing;" />
    <script type="text/javascript"
        tal:define="isDisabled python:test(accessor() and size!=0, 'true', 'false')"
            tal:content="string:document.getElementById('${fieldName}_file').disabled=$isDisabled;">
    </script>
</metal:define>