How to Make a WordPress Thumbnail Redirect to an External URL

1. Copy the URL to your clipboard to which you want to link the thumbnail in your WordPress post.
2. Log in to your WordPress admin account and visit your blog's dashboard.

3. Create a new post or page by clicking the 'Add New' tab under either the 'Posts' or 'Pages' section on the left menu. As an alternative, add the thumbnail to an existing post or page by clicking the 'All Posts' or 'All Pages' tab under the appropriate section. Hover your mouse over the title of the page or post, and then click the 'Edit' link in the menu that appears beneath the title.
4. Click the place in the text of the post or page where you want your thumbnail to appear.
5. Click the 'Image' icon immediately to the right of 'Upload/Insert' above the posting form. A pop-up box appears prompting you to either upload a new image, or insert one you've already uploaded to your WordPress media gallery.
6. Upload a new image by clicking the 'From Computer' tab at the top of the pop-up box, and then click the 'Select Files' button to browse your hard drive for your image. Double-click the image to select it. You can also use an image you've already uploaded by clicking the 'Galleries' or 'Media Library' tab, and then clicking the link that says 'Show' next to the image you want to use.
7. Customize the image details to your liking, including a title, alternate text, description and caption, if you wish. Paste your external URL into the 'Link URL' field. Click the radio button next to 'Thumbnail' in the 'Size' section, and then click the 'Insert Into Post' button to insert the thumbnail into your post or page.
8. Add or edit any additional content to the post or page, including tags, a subject line and other information.
9. Click the 'Publish' button in the right column if you're working with a new post or page, or if you're editing a pre-existing page or post, click the 'Update' button to make your changes live.
10. Check that your thumbnail links to the external URL you want it to by visiting your WordPress blog and hovering your mouse over the thumbnail image. In the status bar of your browser, you should see the external URL you want to link to.