Adobe forum response.

See forum thread http://forums.adobe.com/thread/743954


For <img> tag, value of title attribute is used to display tooltip/screentip for the image. The alt attribute is meant to be used as an alternative text if the image is not available, not as a mouse-over text. In Robohelp, user can specify the screentip for each image. Robohelp(<=9.0) does not have user interface to update/insert alternative text, though user can go to the code view for each image and update the value of alternative text.

 Now your problem occurs in the case when the value of alt attribute is empty. To provide each image an alt value(required for XHTML),  the filename of the image is copied to the alt attribute value on generating output. This filename is somehow converted to absolute path of the image in PDF, that is shown in the description as tooltip.

 One solution to the problem is to copy the value of the screentip to the alt text. Doing this manually will be a tedious task for projects having large number of images. To automate the work, please download a Robohelp script(AltTestUpdater.jsx) from https://acrobat.com/#d=DVsTaYdohOB8T*2woAhBLA and rename it from AltTestUpdater_jsx to AltTestUpdater.jsx


This script can be used to 

1.       Copy the  title attribute of the image into alt attribute when alt attribute is empty.

2.       To force update alt attributes from title, uncomment the line in the script.

//altUpdater.SetForceUpdate(true);

3.       The script will notify the user with the number of updated topics, master pages and snippets in the project once script is executed.
 

Steps to execute the script:

1.       Launch RoboHelp.

2.       Open the project.

3.       Open Script Explorer pod from View>pods menu and import the script.

4.       Please close all the topics, master pages and snippets if any are opened.

5.       Run the Script from the Script Explorer.

6.       You will be prompted with summary iterating how many topics, master pages and snippets got updated.