If you're apt to add images within your works, please read:
A user has uncovered the fact that some images, when linked from Tumblr, will not print out if the work is printed, nor will it export if you save the work as PDF. It works if you save a work as HTML or as ePub, but how Tumblr does their image sharing - which is basically "You can see the image, but you can't really see it because it's hidden behind a frame so you can't do anything with it" prevents it from being exported in certain formats. Printed or PDF.
If you are going to add images to stories - or just share artwork via a SquidgeWorld work, that's absolutely fine. But just know that some providers (and I believe Giphy is another) won't let you actually interact with the image itself, and thus it won't act like other images when exported. If in doubt, you can always use something like MediaFire, or Squidge Image Hosting (link in the "Community" tab across the top) to host your images.