Embeding Tumblr content requires access to the account's dashboard:
Tumbler couldn’t make it easy to embed your blog to your website. Have in mind that what you can bring to your website is the “homepage” of your blog, the posting themselves will stay in tumblr (unless you display them entirely on it). Also you will be only able to do this is you have access to the html files in your site.
Go to your blog and click on “dashboard”
On the top menu go to “goodies”
Look on the right side bar for the last block called “Embed Your Blog”
Copy the script tag
Now, go to your website
Open the html page where you want to place the blog
Insert the scrip tag, exactly where you want the posts to show.
Open your page on the browser and voila! you have your blog right there
Below is an embedded iframe video from YouTube:
Below is an embedded iframe slideshow from flickr:
iFrame code created via flickrslidr.com
Below is an embedded iframe slideshow from imgur: