This issue can occur when your app uses the pub/ directory as the root directory for the Magento installation. This is usually considered a good practice, but it has some drawbacks. The extension can’t know which directory is the root folder for Magento, so it always assumes the base directory is your root folder.
The best way to handle this problem is to make your server ignore /pub in the url.
If it’s not possible to change the server configuration, a setting is provided in Stores > Configuration > Algolia Search > Advanced > Remove /pub/ from image URLs.
Please reindex the catalog after changing this setting.