So, as I usually do when I want something that doesn't exist, I made it myself.
My Lovecraft picture dice is a mini-set of three cubes with 18 iconic images of a Cthulhu-esque nature. I went online with a list of icons I wanted to find and, sticking to simple black-and-white line art, found some suitable artwork to use. I created a template of 20 1-inch squares, and fit each of the 18 images within. I had a set of spare white 6-siders that were 1/2 inch across, so I shrank my template by 50% (so the squares were now 1/2 inch across), then printed it out on a sheet of label paper. I cut out the squares, adhered them randomly to my spare dice, and now I have my own set of Lovecraftian picture dice to use with my Story Cubes. (I also plan to use them with Untold: Adventures Await upon Kickstarter fulfillment.)
Here's the image I created. I'll leave the descriptions of what each represents up to your imagination:
Oh, and if you wish to create your own set of Lovecraft picture dice, you can either grab the image above of download the original PNG file from my Google Drive at this link. Print it off, cut it out, and glue the 18 images to three spare dice. Then roll up some Lovecraftian nightmares of your own!