If you want, you can give each episode its own image. 

If you upload something here, the podcast cover image of this episode will be replaced with the episode image. However, some podcast platforms ignore the image change and always show the podcast cover image. Some do show both images, though.

Your episode cover image should be smaller than your podcast cover image, because it will be integrated into the audio file. 

You can find more information about cover images, sizes and so on here: The cover image of your podcast