As long as you adhere to the amounts that may be copied under fair dealing you may post charts and diagrams from textbooks, or other works, on LEARN. If for example, you wish to post multiple images from a book, you may do so as long as those images amount to no more than 10% of the book (see the Fair Dealing Advisory). It’s important to note that if you wish to post such material to a website that website must be password protected or otherwise restricted to students enrolled in your course.
Please note that just because you acknowledge the author and source of a work doesn’t mean you won’t be liable for copyright infringement. Acknowledging the source is no defence if the way in which you’ve used the work is not permitted under the Copyright Act. So make sure you either fall within an exception or have the copyright owner’s permission.