Where to find the checksums of Ubuntu ISO images?

https://help.ubuntu.com/community/UbuntuHashes

In your case the md5sum is 59d15a16ce90c8ee97fa7c211b7673a8


MD5 & SHA-1/SHA-256 hashes are available in the actual releases folder. Look for the filenames "MD5SUMS" & "SHA1SUMS"/ "SHA256SUMS"

For example:

http://releases.ubuntu.com/16.04/

OR

http://releases.ubuntu.com/17.04/

if you scroll down to the list of files. Downloads & hashes for previous supported releases are also available on releases.ubuntu.com


Take a look here:

https://help.ubuntu.com/community/UbuntuHashes