Mi Yodeya's faq includes a set of guidelines for citing others' work, including the following points:
- Even more helpful would be to also summarize, in your own words, what the external material says.
This helps people get an idea of the answer you're presenting, and also helps them decide whether to follow your reference.
- If there are parts of the external material that would be best quoted in their original language to enhance your summary, you may quote small excerpts, as long as you make it clear that they're quotations using quotation marks or blockquoting.
To do blockquoting, use the button that looks like quotation marks or see here. Be careful when pasting in text; you might need to add some line spacing to make it look right.
These guidelines apply whether the cited work is online or in print. As far as I know, that's the closest we have to an official policy that's relevant. As far as I'm concerned, that's sufficient to indicate that photographs of sources are officially frowned upon.
The following is my opinion and understanding:
There is no need to provide photographic evidence that a book contains the ideas or quotations you cite from it. A clear citation should be enough for someone who wants to check your work.
Many books contain notices along the lines of the following:
All rights reserved. No part of this publication may be reproduced, distributed, or transmitted in any form or by any means, including photocopying, recording, or other electronic or mechanical methods, without the prior written permission of the publisher, except in the case of brief quotations embodied in critical reviews and certain other noncommercial uses permitted by copyright law.1
If such statements are binding, that would seem, to my lay understanding, to create a presumption that posting photos of any part of the book online would be a violation of copyright. I'm not an expert in copyright law, so I don't know if photographing part of a book to prove on the web that you found something there is one of the exceptions.
In any case, photographs of sources are far inferior to quotations from them for another set of reasons: Photographs can't be dealt with as text (e.g. copy/paste of a phrase), can't be searched as text, and are unintelligible to screen-reader software used by blind people (related).
My strong recommendation is to follow our guidelines: cite, summarize, and quote selectively, rather than photographing.
1. Found on The Book Designer website, and typical, to my recollection, of many books.
