This raises an important point about copyrighted material.

In most cases, for private study, one could trace a copyrighted work.
There is, however, no percentage of a copyrighted work that could be included as one's own work if it can be demonstrated that the core concept has been copied.
Copyrighted material can be part of your inspiration, not part of your work.

A fair use challenge comes into play where the originator could possibly show loss of earnings through your copy.

I take my own photos, I design my own sites, I seek out graphics that can be copied, I use my own inspiration (from looking at others' work).

You could trace a monkey from a photo as its features and not copyrightable; ethically, the composition is what you are lifting so don't do it.

The nearest analogy I can think of is I put a Zippo® lighter on eBay and erroneously mentioned it was Zippo-like; the company's lawyers jumped on this within hours. I changed the description and all was sweet.
Think of the fun your clients might have it your built a site with copyrighted material.

Artifex cave,
Acorn