1. Make a project
   
2. Download the project
   
3. Rename to .zip
   
4. Extract
   
5. Overwrite one of the costume images with the image you want to upload
   
6. Zip the project back up and upload into the online editor
   
7. Download it again
   
8. Note the name of the image file with your image
   
9. Append the name to the link https://assets.scratch.mit.edu/w/images/.%2E/.%2E/
   
10. Use that as the image source; for example

    [img]https://assets.scratch.mit.edu/w/images/.%2E/.%2E/ce1b3768c457137501959b784f83e719.png[/img]

gem1001 wrote:

There is a new way:

1. Make a project
   
2. Download the project
   
3. Rename to .zip
   
4. Extract
   
5. Overwrite one of the costume images with the image you want to upload
   
6. Zip the project back up and upload into the online editor
   
7. Download it again
   
8. Note the name of the image file with your image
   
9. Append the name to the link https://assets.scratch.mit.edu/w/images/.%2E/.%2E/
   
10. Use that as the image source; for example

    [img]https://assets.scratch.mit.edu/w/images/.%2E/.%2E/ce1b3768c457137501959b784f83e719.png[/img]

Credit to @redspacecat (I think)

1. so complicated
   
2. where to put .zip
   
3. how to zip up a project
   
4. you are like

   Import computer science