can you use i in a dissertation
If it is not already available to you, obtaining a dissertation may be more difficult than obtaining an article. There are far more articles written than dissertations.
A dissertation is usually the length of a book, perhaps 100 pages or more. scholarly articles are usually much shorter than that.
When using images of others in your own work, you should pay attention to copyright.
Images without copyright or with a license that allows reuse (e.g. Creative Commons) can always be used for any publication. However, remember to cite the source or copyright owner, also in the case of images with a Creative Commons (CC) license.