Fun Numismatic Quiz number one answered.
Insider2
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Sorry, no prizes 
as it takes me over a week to mail them to the winner.
I'm posting the rules NOW so you all can absorb them before the contest starts.
The Non-Contest:
I am going to be posting micrographs of anything that can be found on coins. Some will be easy and some will not. The correct answer is whatever I say it is 
but feel free to disagree (giving your reason) so all of us can discuss it. Images will be posted in this thread at my discretion - several each week. I will post the answers late the next day after it was posted.
In order to make this FUN for beginners I'll ask the "experts" to PLEASE not guess what any of the images are until the next day. Otherwise, folks like (fill in the blank) will get all of them immediately - NO FUN. If no correct answer is given by the next day, the "experts" should PLEASE respond. The answer for each image will usually be posted in the afternoon when I add another image.
The Rules:
- Anyone can guess.
- The BEST correct answer is in two parts. A. What characteristic the image shows. B. What are the reasons, what did you see to determine your answer.
The Example:
The Answer:
The reverse of a cent. I know because it says "One Cent." 
Comments
"The correct answer is whatever I say it is
" HAHAH this should be good!
1
What do you see that is unusual on this coin? What caused it?
Please Note: Before the foolish Jokers' answer, it is not that the coin's image is sideways, the color balance is off, or "show me the edge" Big LOL, NOT! If this discussion generates into that kind of nonsense or trolls
try to wreck it, I'll be very happy to take this attempt to generate some hopefully informative discussions to a different coin forum. 
Edited as I guess I am overqualified
.....
Rubber band.
this is the PCGS boards...
Yes, a thousand times yes! You are one of the "experts" I referred to above in the rules. We'll all look forward to any help you can give - especially in the form of hints the NEXT DAY if the "non-experts" are having trouble identifying the image.
PS No harm done either as I expect several other "experts" answer before reading my request in the rules. I think if the trolls and jokers stay away, in a week, things will be running smoothly and the less informed members will be the first to post guesses.
I am looking at the glitch behind and below Mr Lincolns eye caused by a piece of foreign matter during pressing
Absolutely! We have several members here on CU who can correct any of my errors so we'll all learn something.
I'll probably be posting something that I cannot answer too.
Rubber band sounds good but on first look I thought that stripe was caused by the alloy mixture of the copper the blank was punched out of.
The lines seem to thin out relative to the distance from the heavy band.
"Inspiration exists, but it has to find you working" Pablo Picasso
@chumley said: "I am looking at the glitch behind and below Mr Lincolns eye caused by a piece of foreign matter during pressing."
Great eye-for detail! No one
said there would be only one correct answer or one characteristic in an image! Are we having fun yet?
I’ll be out in the south forty.....
A cent that was taped in an album causing it to tone differently in the center where there was no tape?
vertical strip of toning. Rubber band caused?
bob
It's......nah, never mind...I'll wait till tomorrow
Keeper of the VAM Catalog • Professional Coin Imaging • Prime Number Set • World Coins in Early America • British Trade Dollars • Variety Attribution
The streak from top to bottom, or side to side as we see it, was caused by an alloy mixture.
Are we having fun yet?
A. Horizontal discolorations traveling east to west per the picture’s approximate 90 degree clockwise rotation. Appearance of “pock” marks on Lincoln’s cheek by the eye and by the jaw.
B. Improper alloy mix (horizontal discoloration) and lamination issue (“pock” marks) caused by the improper alloy mix?)?
Edited: To conform to the OP answer format.
Alrighty then, let's get going !!!
Is it a planchet flaw, like improper mixture of metals?
If not I would then guess some kind of copper strike through. Reminds me of the wood grain look some coins get
https://www.autismforums.com/media/albums/acrylic-colors-by-rocco.291/
We need to give the late night posters a chance. I have over 10K images so if this discussion catches on it will take years to finish.
Double Die with rubber ban staining.
I am thinking the metal alloy was not uniformly mixed at the time the metal cooled and rolled to thickness.
A piece of metal such as a piece of wire struck into the surface?
Worry is the interest you pay on a debt you may not owe.
"Paper money eventually returns to its intrinsic value---zero."----Voltaire
"Everything you say should be true, but not everything true should be said."----Voltaire
Improper alloy mix and lamination flaw and Lincoln is looking down at the ground. Peace Roy
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It appears the strip stock was bad. Probably originated at the mill.
Noice!
Unless the poster deletes it as I have asked, PLEASE ignore the post above that has nothing to do with this non-contest!
I will be posting a new image in a few hours w/answers to this one. Several posted the correct answer.
Answer:
Thanks to the members who knew what this "error" was and refrained from posting to let others guess.
This coin resulted from an improper mixing of the alloys use for the cent. What makes it worthy of an image is the straight outline of the discoloration. Several members noticed the squiggle on Lincoln's head where the surface peeled up (lamination).
A discoloration from different exposure to the air due to tape (removed) is a good guess that may explain the straight lines however the lamination argues against this. Additionally, if you look closely, the discoloration has horizontal streaks so NOT due to tape.
What about a reaction to the sulfur in a rubber band? Again, the streaks eliminate that and if a rubber band were in contact with the copper (enough to change the color of the surface) it would become microscopically etched.
Now, I'll be posting another non-contest today. In the meantime, let's see some more copper coins with a streaked alloy surface.