When we run copies there are black lines that print at the top of the page, they go down for about an inch and stop, they get progressively lighter as they get further down the page.

While the line is showing up on the output pages.
Stop printing and put paper in the manual feed tray (tray 1).
Start printing again. As a page gets pulled into the printer about 1/2 way open the top cover.
Pull out the toner and look at the page inside the printer. If it doesn't have the grey/black line, get the fuser replaced. It is defective.

by dragging the black bar on the left with your mouse when
the cursor changes for resize

You might have touched the main charger cleaner a green part above the waste toner container. just push it inside and try to copy and print

This is caused by dirt/debrise on the ADF (automatic document feeder) scanner glass. You need to open up the feeder where your originals are fed in and look for a strip of glass that runs from front to back. It is about an inch or so wide. You need to clean this glass to get rid of the lines. Some models have this glass just to the left of the large main glass, but in your case I beleive it is in the feeder itself.
Good Luck.

try cleaning the rollers with water in the feeder at the top check the glass too too see if it's dirty

there is probably a dirt spot on the scanner glass where the document feeds in. try cleaning the thin glass under the document feed cover.

OK, from the desciption i can assume several things here are some option.
If by receipt you are talking about the confirmation the unit prints the the problem is likely dirty glass.
You would also get the lines when you make a copy using the ADF.
Open the lid there are two areas of glass the thin strip is likely dirty and needs to be cleaned.

If by receipt you mean pages you receive from someone else, and not printed or copied on your machine, then their machine has the condition described above.

If everything has the lines then you have a toner or fuser problem:
This is the test to determine toner or fuser issue.
Print a test page
When you hear the paper feed into the machine open the top to stop the machine
Remove the toner cart.
You should be able to see the page with printing on it. (This is before the page hits the fuser)
If you can see the smudge or marks on the page the problem is most likely the cartridge but NOT the fuser.
If the page is clean the problem is most likely the fuser.
Hope this helps

The small glass surface at the top of the scanner bed had some gunk on it. I scrapped it off and the line went away! Yay!

I had bought a re-inked black cartridge from Staples; although my computer said that the cartridge was full, it wasn't working; I removed and put in a regula 16 black from Staples brand and now everything is fine. Thank you

There must be a strip of glass about one inch wide, next to
the large glass. There is the problem !
Clean that strip thourougly. When you use the feeder the pages
are scanned thru the small strip of glass.