You can use Windows 10 Version 1709 Installation Media which will work with your Windows 7 OEM key printed on the affixed COA or Windows 8/8.1 OEM key embedded in the UEFI BIOS:

http://dellwindowsreinstallationguide.com/download-windows-1709/ 

Dell does not and never has provided Factory Reinstall ISO's.  They also do not provide DVD for reinstall if warranty is expired or windows is no longer supported for XP VISTA 7.   Digital River downloads for Windows 7 ISO are also gone from microsoft.  You can get windows 8 disks from Ebay and Amazon.  Windows 8.1 disks are also out there.  Windows 10 reinstall media is USB Flash.  You can also buy OEM System Builder copies for 7 8 10.  Windows 10 is the ONLY os availble retail and support wise at this point.

https://www.newegg.com/Operating-Systems/SubCategory/ID-368

https://www.newegg.com/Product/Product.aspx?Item=N82E16832588491

https://www.newegg.com/Product/Product.aspx?Item=N82E16832416892

They do not and have not offered ISO's for Inspiron 660s.

W7HP64, USB, WW, MUI, DT
Kit, Software, W7HP64, Universal Serial Bus, World Wide, Multiple User Interface, Desktop

They They do not and have not offered ISO's for systems that are no longer covered under Warranty.

They do not and have not offered Windows 7 Dell OEM ISO's ever and never will.

They did at one time offer a one time use USB flash drive.

This too is now gone forever.

Windows 7 is in Extended support mode until 2020 when its dead.

Dell does not and never has provided Factory Reinstall ISOs.

They may not have had offered ISOs in the past, but they do now.

Using the Service Tag number of a the Latitude E6320 that I bought from DellAuction.com, I was able to download Windows 7 Pro 64-bit directly from Dell using Dell OS Recovery Tool. It took nearly 5 hours on my slow internet connection but I got it. The laptop's hard drive was wiped clean but it originally came with Window 7 Pro 64-bit.

Information at http://www.dell.com/support/contents/us/en/19/article/Product-Support/Self-support-Knowledgebase/software-and-downloads/dell-backup-solutions/Media-backup?dgc=SM&cid=60916&lid=777082590&linkId=33369211

My E6230 is not under warranty unless you count the 90-day warranty from DellAuction.com

I still was able to download the ISO this past weekend.

http://www.dell.com/support/home/us/en/19/drivers/osiso/win

Order Recovery Media

If you prefer to use a physical device, please contact Dell technical support to order a copy. If your product is no longer in warranty, there may be a fee associated with this service.

Although there is some good data in this thread, my apologies for the turn of tone. Since the 2012 Inspiron 660s shipped with an optical drive, my advice is to purchase the Dell OEM operating system CD from this 3rd party.

Although there is some good data in this thread, my apologies for the turn of tone. Since the 2012 Inspiron 660s shipped with an optical drive, my advice is to purchase the Dell OEM operating system CD from this 3rd party.

Why buy when the OP can download his own copy of the ISO for free?

It is all very simple. Enter your service tag #. If there is a download available, it will let you download it.
Very simple. Isn't it?

http://www.dell.com/support/home/us/en/19/drivers/osiso/win

Actually its more complicated than that.  Having a service tag will not let you download media unless you are downloading said media ON THE MACHINE type.  Aka you cant download a 660 media on another kind of dell or worse a non dell machine.  I'm also fairly certain that a government laptop vs consumer 660 have different availability for support and media.

I find it ironic that the 3rd party is using this image.

Easy for some. Some users do not know how to prepare a USB key, move the ISO to it, all the other little steps needed. With a CD, you simply insert it, restart, press F12, choose CD. But again, all good advice on the thread. I just think that several choices for the user is better than only offering one.