I’ve tried to make External Images work automatically on ALL the themes, but there is just so much variety in theme coding out there that it’s just not possible to make it fully automatic.
Some themes correctly use the wordpress functions to grab the thumb or featured image, and in these cases, it will work perfectly straight out the box.
Other themes grab images directly from the database. In these cases, we have to filter their output and replace it with ours. Different themes place these filters on a variety of different hooks.
Other themes even remove the default actions from the main featured image hooks or thumbnail hooks and move the hooks elsewhere.
In these final two cases, to guarantee compatibility with *every* theme, we need to provide:
- An action hook selector for where to place the featured image and a checkbox for whether we should remove other actions from this hook
- Same as above but for thumbnail hooks
- A filter hook selector to override thumbnail generator – we normally get this right, but this may occasionally be required