Many times we consult and read documents (paper, PDF or online) to research information and all the information consulted needs to refer to a list. This list is called bibliography or webgraphy.
It is not an easy task because you need to be so rigourous and always make the same structure. Besides, there are different models and in some places the references are requested in a particular way, e.g., APA, UNE...
In SiX we have this document that explains what a bibliography is and how to do this depending on the type of document consulted.
Remember that you can't use everthing that you find on the Internet. There are images and documents with copyright and we are not allowed to use them without paying or the permision of the owner.
The best option is that you take the photos yourselves or create the images to illustrate your articles.
As well as we have to make reference to the documents, we have to make reference to the images used. At least to link the website of the image.