Well, these images could be data from an app you are using or one you have uninstalled. A few games do download a lot of data and they like to use the "SD card" if one is available (this is how Android sees the partition that the Fire refers to as "Internal Storage") because on a phone that would be where the majority of storage is located. If they appear in a directory named after an app you know you uninstalled, then I would say it's safe to remove the whole thing. Otherwise, probably not.
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