Hi arctic,
The answer depends on where you live. You spelt the word 'color' the American way which makes me wonder if you are based in the USA. Since i don't know for sure I will cover this from both the UK and US perspective.
UK
Under UK law the thesis you have written would be covered by the fair dealing exception for
research and private study and so you do not need permission to create and use the adaptations, just credit the original source. You could do this with a footnote or endnnote. It is probable that the exception for
educational instruction would also apply, since I assume this thesis is connected to a degree or PhD or something similar. If you intend to publish your thesis at some later date, that would be the time to get copyright clearance.
USA
Here you can take advantage of the US
Fair Use provisions, which like the UK, cover exceptions for the purpose of education and academic research. In particular fair use includes a concept known as transformative use which would undoubtedly apply here. In theory publishing your thesis commercially at a later stage would slightly alter the evaluation of the four factors used in determining fair use, but I think that on balance your use of these images would not in any way damage the commercial value of the originals, and so you can discount that. Unlike the UK's fair dealing, fair use does not require acknowledgement of the source, although I think that in view of the scholarly nature of the work it would be appropriate to cite them anyway to avoid any suggestion of plagiarism.
I should mention for the sake of completeness that under
§106A(a)(2) of the Copyright Act 1976 the author of a work of visual art has the right not to have his/her name attached to any distortion or mutilation of his work. I'm not sure if transforming these images into line drawings would amount to distortion or mutilation (in a legal argument), but if you merely cite the article or atlas title you would not be attaching the artist/photographer's name so this provision won't apply.
