Importing posts and images from one website into another with the WordPress Importer and Auto Upload Images plugin

Step 1: Prepare your export file on the old site

On your old website go to 'Tools > Export' and export your posts only.

Step 2: Import your posts into the new site

On your new website go to 'Tools > Import' and import the posts you exported. The importer has an option to download and import file attachments, but this won't work if you're not migrating all content, so you can ignore this.

Step 3: Install and activate the Auto Upload Images plugin

It installs as any other plugin in the WordPress repository. Once activated the plugin adds a settings page under 'Settings > Auto Upload Images', but in my experience you can leave these to their defaults.

Step 4: Get the image from your old site into your new site

At the time of writing the plugin has no option to automatically go through your posts and bulk upload plus update all the images. Instead, it updates each post individually when you save it. If you have many posts this is a lot of work, but there is a little trick. You can go to your posts overview screen and bulk update your posts. There is a little more information on this here (useful note on multisite).

Essentially, you select multiple posts and then under 'bulk actions' choose 'edit' and press the 'apply' button. Then, without making any adjustments, click the 'Update' button. Depending on your server you may get a timeout as the process runs, so it's a good idea to do this maybe 20 to 50 posts at a time.

Step 5: Check your posts and deactivate/uninstall the plugin

When all is done you can check your posts and confirm they now reference local images. You then no longer need the plugin and you can safely deactivate and delete it.