I've seen this being used but how though?

1. Import an image into a Scratch project (or draw one)
2. Save the project to your computer
3. Rename it to a .zip file
4. Copy the name of the file you want to upload on the forums (it might take a while!)
5. Click on the image button, then type: "https://assets.scratch.mit.edu/get_image/.%2E/". Paste the file name afterwards, then press enter.

If you have done everything right, your chosen image will have worked!