There are several free extensions available on the Magento Marketplace that can help you to provide a downloadable link for all product images in Magento 1.9. Here are a few examples:
Product Images Export: This extension allows you to export all product images to a zip file, which can be downloaded by the customer. You can also choose which images to export and customize the file name.
Image Gallery and Product Gallery: This extension creates an image gallery for your products and allows customers to download all images in a zip file. It also includes a product gallery feature, which allows you to add multiple images to a product.
Multiple Images Uploader: This extension allows you to upload multiple images at once and then provides a download link for all images. It also includes features like bulk image upload and drag-and-drop functionality.
You can search for these extensions on the Magento Marketplace and install them on your site. Once installed, you can configure the settings and provide a download link for all product images.