Is it likely that any of our ancestors looked identical to us?

Entirely possible

My friend has an adult son in his early 20s. 

When an elderly unmarried uncle died, she went to help another relative clear the house. They came across some photos and started to go through them. 

She nearly had heart failure when she came across a photo ...... She thought for a minute why is there a photo of my son here.... It was like one of those old fashioned ones you can get at fairgrounds etc..... Then she realized it wasn't her son.... But the man in the photo was his double. Same dark curly hair worn over the collar, same beard, same smile.... Later investigation discovered that the man in the photo was the uncle's grandfather and it dated from the 1890s

Not identical but very close resemblance. I have seen it. You can even find those with no known relationship  (living and/or dead) that look alike or look related.  

I look almost identical to a 2nd cousin of mines more so than with my siblings. 

Very unlikely They may bear some resemblance, but the unique combination of genetic material in each generation will give a different result each time.

It seems very unlikely since you share only 1/8 of your DNA with your great great-grand parents, and even less from your great great-grand uncle/aunt.

It can happen but isn't highly likely.

Genetics is biology not genealogy.............

Identical? Probably not. But if all of your ancestors came from the same geographical area, they might be more likely to look like you because they'd be passing down similar genes.

That'd depend a lot on just how inbred your ancestors are.

EXACTLY? No, not very likely. 

Identical?  No.  Even so-called identical twins are rarely perfectly identical. However, you can certainly resemble, even strikingly, one of your ancestors.

My sister looks very like one of our great-grandmothers.  She doesn't look exactly like her, but I was really amazed the first time I saw a photograph of our great-grandmother as a teenager, because she looked so much like my sister at the same age.