How do I add a Flickr feed to Tumblr?
Some Tumblr themes support Flickr widgets that display your most recent Flickr photos right on your blog. The coolest thing about this is that because they're built right into the blog, they're already made to look great. For example, Vanity's Flickr widget has its own dedicated page, and it really gives the attention to your Flickr photos. Other themes like Fluid give it less emphasis. This post will quickly help you activate the Flickr widget on your blog.
Make sure your theme supports Flickr integration
From your Tumblr dashboard, click on the dropdown menu on the right-hand side that is labelled with your URL and your primary blog's name and choose the blog you want to add a Flickr widget to. Click Customize and scroll down through your customization setting until you see a Flickr User ID field. If there isn't one there, your theme doesn't natively support a Flickr widget.
Retrieve your Flickr User ID
In another tab or window, go to idGettr. If you're not sure what your Flickr username or URL is, log in to Flickr to double-check before continuing. Next, enter your Flickr URL into the idGettr form and click submit. Finally, copy the ID number that appears below the form.
Enter your Flickr User ID into your theme's customization settings
In your customization settings, scroll down to the Flickr User ID field and paste the ID you just retrieved. After previewing and saving your theme, your Flickr widget should be activated.