image markdown fix for the README

README.md

@@ -65,8 +65,7 @@ policy against all incoming SSH connections so that SSHD cannot be scanned, but
 SPA daemon reconfigures the firewall to temporarily grant access to a passively
 authenticated SPA client:
 
-![alt text][SPA-basic-access-SSHD]
-[SPA-basic-access-SSHD]: doc/images/SPA_basic.png "Basic SPA usage to access SSHD"
+![SPA-basic-access-SSHD](doc/images/SPA_basic.png) "Basic SPA usage to access SSHD"
 
 fwknop supports the above, but also goes much further and makes robust usage of NAT
 (for iptables/firewalld firewalls). After all, *important* firewalls are usually gateways
@@ -80,8 +79,7 @@ Because fwknop integrates with NAT, SPA can be leveraged to access internal serv
 applications on modern traditional networks, it also allows fwknop to support cloud
 computing environments such as Amazon's AWS:
 
-![alt text][SPA-Amazon-AWS-cloud]
-[SPA-Amazon-AWS-cloud]: doc/images/SPA_AWS_network_setup.png "SPA usage on Amazon AWS cloud environments"
+![SPA-Amazon-AWS-cloud](doc/images/SPA_AWS_network_setup.png) "SPA usage on Amazon AWS cloud environments"
 
 ## User Interface
 The official cross-platform fwknop client user interface *fwknop-gui*
@@ -90,8 +88,7 @@ is developed by Jonathan Bennett. Most major client-side SPA modes are supported
 including NAT requests, HMAC and Rijndael keys (GnuPG is not yet supported), fwknoprc
 stanza saving, and more.  Currently fwknop-gui runs on Linux, Mac OS X, and
 Windows - here is a screenshot from OS X:
-![alt text][fwknop-gui-OS-X-screenshot]
-[fwknop-gui-OS-X-screenshot]: doc/images/fwknop-gui-OSX.png "fwknop-gui on Mac OS X"
+![fwknop-gui-OS-X-screenshot](doc/images/fwknop-gui-OSX.png) "fwknop-gui on Mac OS X"
 Similarly, an updated
 [Android client](https://github.com/jp-bennett/Fwknop2) is
 [available](https://incomsystems.biz/fwknop-gui/android.php) as well.