Adapt a bunch of alt tags

wiki/src/install/inc/overview.html

@@ -93,13 +93,13 @@
   <div class="row">
     <div class="col-xs-12 col-sm-2 windows linux mac-usb expert">
       <div class="thumbnail">
-        [[!img install/inc/infography/download-and-verify.png link="no" alt="ISO image downloaded and verified"]]
+        [[!img install/inc/infography/download-and-verify.png link="no" alt="USB image downloaded and verified"]]
         <p>Download</p>
       </div>
     </div>
     <div class="col-xs-12 col-sm-2 upgrade-tails">
       <div class="thumbnail">
-        [[!img install/inc/infography/download-and-verify-in-tails.png link="no" alt="ISO image downloaded and verified"]]
+        [[!img install/inc/infography/download-and-verify-in-tails.png link="no" alt="USB image downloaded and verified"]]
         <p>Download</p>
       </div>
     </div>
@@ -111,13 +111,13 @@
     </div>
     <div class="col-xs-12 col-sm-2 windows linux mac-usb expert">
       <div class="thumbnail">
-        [[!img install/inc/infography/install-tails.png link="no" alt="ISO image installed on USB stick on the right"]]
+        [[!img install/inc/infography/install-tails.png link="no" alt="USB image installed on USB stick"]]
         <p>Install</p>
       </div>
     </div>
     <div class="col-xs-12 col-sm-2 upgrade-tails">
       <div class="thumbnail">
-        [[!img install/inc/infography/install-upgrade-usb.png link="no" alt="ISO image installed on USB stick on the left"]]
+        [[!img install/inc/infography/install-upgrade-usb.png link="no" alt="USB image installed on USB stick on the left"]]
         <p>Install intermediary</p>
       </div>
     </div>
@@ -150,7 +150,7 @@
     </div>
     <div class="col-xs-12 col-sm-2 windows linux mac-usb install-clone mac-clone expert">
       <div class="thumbnail">
-        [[!img install/inc/infography/create-persistence.png link="no" alt="Encryption configured on USB stick on the right"]]
+        [[!img install/inc/infography/create-persistence.png link="no" alt="Encryption configured on USB stick"]]
         <p>Configure</p>
       </div>
     </div>

wiki/src/install/inc/steps/install_with_etcher.inline.mdwn

@@ -29,7 +29,7 @@
 1. Etcher should automatically select your USB stick. Otherwise, click the
    <span class="button">Change</span> link to choose a different USB stick.
 
-   <div class="step-image">[[!img install/inc/infography/install-tails.png link="no" alt=""]]</div>
+   <div class="step-image">[[!img install/inc/infography/install-tails.png link="no" alt="USB image installed on USB stick"]]</div>
 
 1. Click <span class="button">Flash</span>.
 

wiki/src/install/inc/steps/install_with_gnome_disks.inline.mdwn

@@ -17,7 +17,7 @@
 
    <div class="step-image">
      [[!img install/inc/infography/plug-usb.png link="no" class="linux" alt="USB stick plugged in the computer"]]
-     [[!img install/inc/infography/plug-upgrade-usb.png link="no" class="upgrade" alt=""]]
+     [[!img install/inc/infography/plug-upgrade-usb.png link="no" class="upgrade" alt="USB stick plugged on the left"]]
    </div>
 
 1. Plug in the <span class="upgrade">intermediary</span> USB stick <span class="linux">on which you want to install Tails</span>.
@@ -29,8 +29,8 @@
    [[!img install/inc/screenshots/gnome_disks_drive.png link="no" alt=""]]
 
    <div class="step-image">
-     [[!img install/inc/infography/install-tails.png link="no" class="linux" alt=""]]
-     [[!img install/inc/infography/install-upgrade-usb.png link="no" class="upgrade" alt=""]]
+     [[!img install/inc/infography/install-tails.png link="no" class="linux" alt="USB image installed on USB stick"]]
+     [[!img install/inc/infography/install-upgrade-usb.png link="no" class="upgrade" alt="USB image installed on USB stick on the left"]]
    </div>
 
 1. Click on the

wiki/src/install/inc/steps/restart_first_time.inline.mdwn

@@ -48,7 +48,7 @@ the rest of the instructions afterwards, we recommend you either:
 
 <div class="step-image">
 [[!img install/inc/infography/plug-other-tails.png link="no" class="clone" alt="USB stick plugged on the left"]]
-[[!img install/inc/infography/restart-on-tails.png link="no" class="windows linux mac-usb" alt="Computer restarted on USB stick on the right"]]
+[[!img install/inc/infography/restart-on-tails.png link="no" class="windows linux mac-usb" alt="Computer restarted on USB stick"]]
 [[!img install/inc/infography/restart-on-other-tails.png link="no" class="clone" alt="Computer restarted on USB stick on the left"]]
 [[!img install/inc/infography/restart-on-upgrade-usb.png link="no" class="upgrade-tails" alt="USB stick unplugged on the right and computer restarted on USB stick on the left"]]
 </div>