Working on a friend's web site and came up with a whole list of errors in the source code. I fixed some of the major stuff. But I'm having problems with site because it is dynamically driven with a bunch of plugins. I wanted to scream because this all of this stuff should have been worked out by the designer who she paid a bunch of money.

OK enough rant. Here's the problem. I want to find the plugin responsible for some slideshows on the index page and some of blog posts so I can add alt tags to the images but when I look in the plugins I can't find the plugin that is responsible for generating slide show. When I go to edit the page it shows the plugin but not the actual HTML to be edited. I'm not sure where to look for the plugin.

Are you sure it is a plugin? It could be part of the theme you're using.