For Products you need to create a new Library to add the images. 

Go to Content > Images 

1. Create new library 
2. Set the thumbnail image sizes to library 
3. Go to menu and select the library. 
4. In the bulk actions select the Library properties 

5. Expand “Advanced Options”  

6. Click on the thumbnails sections and selects the thumbnails sizes. 

7. Save Changes. 

Now you can upload the products, catalogs, or attributes images.