Trying to make image "ads" for Facebook

Apparently a lot of authors get really good results by sharing posts through Facebook reader posts. I'm friends with some of them, and like clockwork, several times a week, they all post the same image, book links, etc to a series of reader groups in a row. I was skeptical that they get sales that way, but at least one told me that sales actually go down when she takes a week off from doing it, so I thought I'd put aside my "ugh, so spammy" reservations and try and make a few things to share on Facebook. 

The following are my "attempts" to make some share-able book ads for my various books.

For my Dragon and the Scholar Saga, specifically Dragon's Curse

This is my "flagship" book. It's what I sell the most copies of. It's the gateway to my series, and I have it at the tempting price of 99 cents. I have NO idea why the font comes out so fuzzy in image number 2 though. I need to work on that. 

This one is my attempt at humor. "Reasons why you should NOT read Dragon's Curse."

For Thaddeus Whiskers and the Dragon

This book is aimed at younger readers, and this makes it harder to market. For one thing, younger readers tend to read paperback rather than ebook, so I made this one to advertise a coupon code for the paperback version of the book. I used the lovely painting my illustrator did, which my cover artist had to crop severely to get the book cover format right, so I'm glad I have a reason to share the full image. 

I also borrowed an Ogden Nash rhyme to promote the book.

And here is one for the ebook sale I did March 16th through 20th.

And finally for Beggar Magic

With Beggar Magic I went with reader quotes, but I haven't been able to figure out a snappy tagline to make any more images for it. Maybe soon.

Honestly, these things are a lot of work to make and I'm not sure they get results. I'm not good at the advertising part of this. 

Sales are still steady, but I feel like I should always be doing something to keep the momentum up. 

Feel free to share any of the images above ;). 
Have you had any luck with making ad images?