What is the difference between the ruling on earning money from cracked software that has been deemed permissible, and the ruling on using paid images that are widely available for free and have been deemed impermissible, even though both cases involve using something that was not originally free?

The ruling on an action, in terms of its permissibility or prohibition, is one thing, and the ruling on the wealth earned from it is another. An action might be forbidden, yet the profit generated from it is permissible. An example of this is using non-free software without the permission of its owners; it is not permissible to use it, but what is produced from it is the effort of its owner, and his profit is permissible for him.