You can take a look at this Amazon Product Advertising API (btw it demands you to have as AWS account), it provides possibility to look for book, probably in your case it will fit.
Alternatively you can read Amazon API: How To Get A Book’s Image - there is described how to get image of book, but together with that information you get ASIN, and as written in Wikipedia for 10 digits it is the same as ISBN. That example was written in PHP, but I'm sure you can port it to Python. On the other hand, Accessing Amazon’s Product Advertising API with Python gives you code sample to access AWS using Python (but without such a good description of what is going on there, as those articles about AWS+PHP, I advice you to read them for better understanding)
Here is a list of services you can try as alternative to Amazon API.
