Copyright protection of original creative expression is automatic to the author. That means that any blog post, essay, photograph, etc., you have created and saved on the computer, packed away in a closet, or posted online is protected by copyright. Unless your creation was made under contract or within the auspices of your job, you remain the copyright owner for life plus 70 years or until you decide to sign over your copyright ownership to someone else. This signing over of copyright happens often during the publishing of scholarly articles, or you could choose to forfeit your copyright ownership and gift your creation to the public domain.
2. You can cite your sources and still infringe on copyright.
Plagiarism, or including someone else's work in your projects without giving them proper credit or citation, and copyright are related but different concepts. Since copyright law gives to creators the exclusive rights of copying, distributing, making derivatives, displaying and performing their works, you could properly cite a source and still infringe on copyright by using too much of something, sharing it too widely and without permissions, performing it without a license, etc. Most of the time you are quoting someone else in your paper, you are relying on an exception to copyright law called fair use. The fair use exception says that some uses of copyrighted content are not infringements, like scholarship, teaching, and criticism, as long as they take into account four factors. These factors are 1.) the purpose of the use, if it is research, teaching, etc; 2.) the nature of the original, where fictional and creative work gets stronger protection; 3.) the amount used, which is typically small in a quoting situation; and 4.) the effect of the use on the commercial market of the original.
3. Easily accessed images online are probably still copyright protected.