This is actually a cheat and not a true embed.

1. Go to your infogr.am infographic.
2. Hit the blue “Share” button at the top right of the screen.
3. In the Publish dialog box that pops up hit the dark gray “View on web” button. You’ll see your infographic as others would see it.

Now the cheat part.

1. Using a screen grab tool (Grab on the Mac) Select part of the info graphic and grab it. Save it with a name and to a location that you can find it. (I called mine “infographic”and saved it to the desktop.)
2. Double click the image on your desktop. It should open in Preview.
3. Select File / Save As in Preview and select PNG from the Format drop down. Hit Save.
4. Back to your WordPress Post. Select the Add Media button above the top left of the editing box.
5. Select Upload Files, find your info graphic file and upload the .png version.
6. At the bottom left of the screen select the “Insert into Post” button. Your graphic will appear in your Post.
7. Last step. Select the graphic in your post.
8. In the top menu select the Link icon and paste the URL for your infogr.am infographic in the URL box. DONE!

See how mine looks.