I'm using WpeMatico plugin which saves images in the post using:

$attach_id = wp_insert_attachment( $attachment, $filename, $postid );

I looked inside wp-includes/post.php > wp_insert_attachment function, but couldn't quite figure how to resize images. I want ALL/ANY images to have a max size of 1024 resize proportionately. I also have the resizing function, just not sure how to use it.


1 Answer 1


The original image size (i.e. 'full') is never modified. Intermediate image sizes are controlled in various places:

  1. Default image sizes ( 'thumbnail', 'medium', 'large' ): core settings, via Dashboard -> Settings -> Media
  2. Custom image sizes: Theme functions.php file, via add_image_size()
  3. Post Thumbnail size ( 'thumbnail' ): Theme functions.php file, viaset_post_thumbnail_size()`

By default, the 'large' image size is constrained to 1024px. So, you can simply output this image size where you need a 1024px image.

If you need to create a custom image size, you'll just need to regenerate thumbnails for existing images.


If you need/want to constrain the size of the 'full' image size, then you'll need to modify it during the upload process, i.e. by hooking into wp_handle_upload, and performing the resize.

There are various Plugins that accomplish this. A quick search turns up:

  • All the options you mentioned resize the image only for DISPLAY, they don't actually "resize" the image to those dimensions, right? I want to resize the image on upload to reduce file size.
    – Nimbuz
    May 14, 2012 at 16:53
  • See edited answer. May 14, 2012 at 17:15
  • Thanks, but again, those plugins won't help me because WpeMatico is uploading those images programmatically, I'm not uploading them manually myself so I could use those plugins.
    – Nimbuz
    May 14, 2012 at 17:21
  • Use a different Plugin, then? Or just use the core UI for image attachments? May 14, 2012 at 18:41

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