Scratch

Did you know you can import tons of images at once into Scratch?
If you did, you probably knew it took really long. Here's the solution!

Open your folder containing all the images (or one animated gif).
Open Scratch, create a sprite to import the images (you can draw a scrible)
Make sure your on the scripts tab, not the costumes tab.
Drag the image(s) from your folder into the scripts panel. Scratch will not react for a few seconds, depending on the size/number of your image(s)
All images will be imported as costumes separately.