How to update the img Title field while uploading it?

Have you confirmed if your theme even uses the title field? Most do not. What’s most important for SEO and screen readers is the alt field. Both fields can be overridden when inserted, so the values used on upload are more like suggested default values.

What issue are you hoping to solve by making the title blank? It likely makes little difference one way or the other. I think it can be made blank via filter when the image meta data is generated. If it’s really that important a need, I can investigate further from you.

Thanks for the detailed clarification. It was a lot more than I had expected 🙂

I was thinking such data was all saved in post meta data, but it turns out most fields are saved in normal post fields of the related attachment post. The title is in post_title naturally, only the alt text is in post meta (meta key _wp_attachment_image_alt). For completeness, the description is in post_content, caption in post_excerpt, attachment slug in post_name.

Making the title field blank makes the media list table display less useful, but at least the filename still appears, so it’s not entirely awful. The title and other post data can be altered prior the image’s attachment post being inserted through the “wp_insert_attachment_data” filter.

Most meta data can be altered prior to insertion through the “add_post_meta” filter. I’ve not tested, but the _wp_attachment_image_alt data can very likely be altered through this filter. There may be a more specific filter somewhere, but this should do. Your callback just needs to ensure it’s only altering the intended value and not any other.

I suggested an inappropriate meta data hook for blanking the alt field. I’m trying to blank out the data before it gets inserted, but am having trouble finding a good hook. It’s feasible to use the very generic “query” hook, but targeting the right query is an inherently weak process. Or we could blank it out after it’s inserted, except such a process is prone to race condition issues. There’s has to be a better way. I’ll dig further when I have more time and get back to you.

As for the title, untested, but something like this:

add_filter('wp_insert_attachment_data', 'gh_blank_title');
function gh_blank_title( $data ) {
  $data['post_title'] = '';
  return $data;
}