Make sure your cron job is set to run each day at less than every 24 hours to be in compliance with Amazon’s TOS regarding image storage as per the following:https://affiliate-program.amazon.com/help/policies?ref_=pe_584750_33951330#Associates
Program IP License
(h) You will not store or cache Product Advertising Content consisting of an image, but you may store a link to Product Advertising Content consisting of an image for up to 24 hours. You may store other Product Advertising Content that does not consist of images for caching purposes for up to 24 hours, but if you do so you must immediately thereafter refresh and re-display the Product Advertising Content by making a call to the PA API or retrieving a new Data Feed and refreshing the Product Advertising Content on your application immediately thereafter. Unless otherwise notified by us, you may store individual Amazon Standard Identification Numbers (ASINs) for an indefinite period until the termination of this License. Notwithstanding the foregoing, if your application includes a client application, the client application may not store or cache Product Advertising Content. Upon our request you will, within three business days of our request, furnish us with a copy of any client application that includes or uses Product Advertising Content for the purpose of verifying your compliance with this License.