What do you think? Can we deep-link to other resources as long as we mention the source? Or should we use only links to point to other resources?
In general I would say linking is perfectly acceptable (and citing sources for any answers should always be encouraged)
However, as a general rule I try to ensure that the question is answered within the text of my answer. I then often offer a link for further extended information.
Specially, with regards to your cited answer I would say that you have answered the question in your own text so that is fine, but unless you have permission you should link to the blog post rather than direct linking the image.
So in summary: yes links in support of an answer are fine. Links on their own I think should be discouraged. Without permission prefer linking to pages rather than resources.
The web is defined by linking; I'd be concerned if we couldn't link to public external resources like that. We aren't (hopefully!) copying and hosting the image, we're just linking to it. (And hopefully crediting the source, out of respect.)
The bigger concern I'd have with including content from external sites like this is one of long-term availability of the content; if lightroomkillertips.com is ever shut down or sold, the link could become invalid (or worse). Or, someone deletes a particular image from the Flickr photostream, etc.
It's an issue on all of the Stack sites, though, and a quick search for "external images" on meta.so turned up a few threads (note the first one, in particular, which covers the idea of being able to attach images to SO posts as a feature request, something I think this community could benefit from immensely):
- Please allow image uploads directly onto the site.
- Official position on the use of images in questions and answers
- Answers with external references; should they not be added to answers and (perhaps) contribute to reputation?
- Image hosting for Stack Overflow answers?
...etc. :) So, my position would be: deep-linking ought to be just fine (it's the foundation of the web), but we may want to encourage avoiding it for the purely pragmatic reason of the content not necessarily being available indefinitely.
I think it depends greatly on the source, and following their rules; so Flickr may be acceptable, as long as the photo links through to the Flickr page for it, but linking through to use another site's glossary may be seen as unethical.
I always revert back to the "how would I feel if someone did it to me" test, and think that works well, and would discourage most usage without prior permission (after all, I have a question about discouraging usage of photos without permission).
Copyright licensing is also a factor.
Content on the site is automatically licensed as Attribution-ShareAlike. If the content you are including is not already under a similar, compatible license and you do not have permission to make it so, you should not include it in your answer.
Deep linking is ambiguous here, but it is reasonable to consider a post which features embedded images linked from a different server to be a derivative work, even if the images are technically only included by reference.
I'm not a lawyer; I'd just prefer the site to stay far on the clean side of things here. If there's an image that would help illustrate your point but doesn't fit the above, point to it with a hyperlink.