Where are the official microsoft ISO's for windows 10 preview?

Question

Hi All,
Where are the official Microsoft ISO's for Windows 10,  10051 and 10056 preview?   They are all over the web, but I don't trust them unless they comes from Microsoft itself.
Many thanks,
-T

Answer 1

To ToddAndMargo,
RE : Is there a way to manually go to Windows Updates and manually download a particular file
No. All updates will be downloaded and installed automatically. You don't get to choose which to install and which to decline.
RE : And I can't find 10049's ISO either (from Microsoft). 
As of now, the only most current ISO available is for build 10041. Build 10049 ISO is not yet available.
When build 10049 is released from Slow ring, usually it is also the time its ISO will be released.
RE: ESD file. How?
One cannot download an esd file of build 10049 from Windows Update.
You download and install the entire build 10049 via Windows Update. When it is done, you can then find its Installed.esd file from RecoveryImage folder and use it to manually create an ISO fie. You will need a specific program to create an ISO from Esd.
You might ask " why do I need an ISO fie if the operating system is already installed ?"
Some users are advocates of "clean install". They prefer clean install over upgrade install. Clean install can be done by burning the ISO file into a bootable DVD or an USB with at least 4 GB capacity and use it to install.
You can also use the same media and install in another compatible computer.
It can also serve as an emergency backup incase you need to reinstall.