There are use cases for Storage API where Image module is not needed. Is it possible to add checks for the Image module function calls and remove the image module dependency?

Information about checking if function from another module exists:
See https://www.drupal.org/node/219100.

I think using module_invoke function should be considered. Note that argumenta are not passed by reference in all PHP versions. See https://api.drupal.org/comment/3359#comment-3359.