Basketball: Hidden changes in iconic Michael Jordan NBA image

Artist Keegan Hall crafted this masterpiece. Photo / Instagram

Artist Keegan Hall's free-hand pencil portrait has wowed the NBA world with an insanely detailed sketch of Michael Jordan's iconic free-throw line dunk.

However, the American artist has revealed he secretly changed details in the crowd to write himself into NBA history.

Hall's decision to take liberties with the iconic image of Jordan taking to the skies during the 1988 NBA Dunk Contest means the artist has drawn himself and several Nike executives, including Nike founder Phil Knight, into the front row of the stadium.

Using a creative license, Hall revealed on Instagram he also snuck in several other NBA identities into the picture.

"I was surprised how many people noticed that I added some different faces from the original image," Hall posted.

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A post shared by Keegan Hall (@keegan.hall)

"The hardest part was drawing all of the people as slightly out of focus / blurry since it would've been much easier to draw them in sharp clarity.

"The area that was noticed most often were the people sitting at the scorer's table in the lower right corner of the drawing."

Hall has since revealed he spent more than 250 hours on the masterpiece.

It is so good, many fans across the world have refused to believe it was a free-hand production.

Hall then released a time lapse clip of his creation being brought to life.

It's easy to see why it went viral earlier this month.

An image of the completed canvas took off on a Reddit forum and quickly turned Hall's piece into the most talked about thing in basketball.

He told USA Today this week his artwork has only recently become a serious consideration for him after years of casual drawing.

It was the death of his mother in 2015, that saw him return to his pencil creations.

It is a decision that has seen Hall raise more than $US450,000 through art sales on his website.

"Art was never part of the plan, but every time I thought I would fail, something kept pushing me forward," Hall told USA Today.

"Losing my mum rocked me to my core, and it's what got me back into drawing to self-medicate through the grieving process. She's what kept me in drawing, too."

Now the whole sporting world wants him to keep drawing.