Three key sites were used to check if the icon already existed.  They are used widely for plagiarism checks – or more positively uniqueness.   They offer a 99% certainty that the image was not already posted on the web.
Google Images

Kefiweb Kefilinkicon Google Images Screenshot

Tineye

Kefiweb Kefilink Image Tineye Screenshot

Yandex

Kefiweb Kefilinkicon Yandex Screenshot