While I agree that logomaker is easy to use, you need to know what you're doing since the EZ Reader only shows (I think) 4 shades of gray. If you look at a color image on your computer, it won't look that good on the reader.
That said, there are ways to optimize the reader's display of your image and as Shel said, if you know computer graphics, it isn't hard.
This is the one I use.
https://www.mobileread.com/forums/album.php?albumid=54&pictureid=1434
And I always have trouble adding images on MR posts, so you can open the URL if you want to see it.