When I read a (math or statistics) textbook, sometimes I do not understand some of the equations or proofs in the book. Is it OK to take a picture of the page in the book (or ebook) that has the equations or proofs, and include it in the question as a supplemental matreial? Does this violate any copyright law?
I'm not a lawyer, so I can't really answer whether a certain use is a violation of the law. I can explain why putting such pictures in your questions may not be a good idea.
One problem with using pictures instead of text to explain your question is that they aren't searchable, so other people with the same question you posted won't be able to find the answers as easily. Another problem is that people with visual impairments may not be able to understand your question if most of it is described by a picture.
It would be best to try to transcribe or summarize the material that you want to take a picture of. You can include the picture as well (but be sure to put something meaningful where it says "enter image description here" and to include which book the picture is from) but your question should be able to be understood without it.