Currently looking to test out installing Windows 10 and one stumbling block was just getting hold of an official disk image. (I'm cautious these days and want to see how setting up a dual boot encrypted Windows 10/Ubuntu goes on a spare drive prior to actually committing to an upgrade.)
Start me up
The obvious searches for installing Windows 10 inevitably lead you to this page where it tells you to install the Media Creation tool and use that.
Critically, that's not an option if you don't have access to a current Windows install. (Yes, it should be easy enough to find a Windows PC somewhere around, but there might not be one to hand.) The other drawback is that, as far as I can see without testing, is that it only creates media for one particular version of Windows, so you'd have to run through the process twice for Home and Pro. The actual ISO disk image is buried on the site under "Tech Bench".
Though the filename differed, the 64-bit download from that page did match the SHA1 as listed on the MSDN site as of 2015-10-23:
File Name: en_windows_10_multiple_editions_x64_dvd_6846432.iso Languages: English SHA1: 60CCE9E9C6557335B4F7B18D02CFE2B438A8B3E2
Note that there's a 90-day Win10 Enterprise trial, but there was no checksum at all to verify that download, and you need a Microsoft account just to get to the download. It also had the following ambiguous information:
In order to use Windows 10 Enterprise, you must sign in to your PC with a Microsoft account. The option to create a local account will be made available at the time of the final release.
which was unclear as to whether this still applies or not.
Clean installing Windows 10
The other question I had was which version, Home or Pro, gets installed from this single ISO. If it's a clean install, how is the version to install (Home or Pro) determined? From what I remember reading, the answer should be that if you skip entering a product key on request by the installer (which would automatically install the appropriate version if you provide a key), the installer prompts you to choose the version to install.