Can you move the image collecting logic into a DLL that can be replaced? Maybe even make it pick up any such DLLs from a plugin folder? It might be worth allowing people to swap out the logic for a proper Google API call with their private API key or for interfacing with other websites.
I have not worked with Unity but I know how to create such a plugin system in dotnet C#. I figure the interface would be a simple factory function to create a result set object implementing IDisposable with the given search query, a set of functions for getting different data, and the inherent Dispose function of an IDisposable for cleanup.