The other thing is people can always ask the creator to use an image. I would be happy if people asked me and would let them use them but nobody ever does actually ask. Anyway most of my photos are portraits so they probably aren't the kind of photos most people want to use.
That's a very good point. Some users would like to see their work used by others, some not so much. I would also suggest asking before using another steemit members youtube video, that could lead to hard feelings.
Yes I think it is just politeness.
It would be great if creators who like their work to be used by others would explicitly state the terms of reuse, e.g. by specifying an appropriate variant of the Creative Commons license. And maybe we can agree on common tags for reusable content.
Actually this could potentially be built into Stemit itself so that people could label each image with the correct tag (separate from the regular 5 tags). That would make it more convenient and would also make people stop and think before they use images.