Automatically generates a caption for images based on the IMG title attribute.
Just omit the title attribute.
No. Just be aware that if the image has a title then it will be affected by the plugin.
By default the plugin works on all your posts, and you've probably been using the IMG title attribute in your old posts. Just set the plugin start date to a date after your old posts and your new ones will be the only one's affected by the plugin.
The plugin folder contains the CSS file for the captions. Modify as you'd like. I've included an image folder there as well, so you can put any background images you want in there, too.
If you want to prevent an image from being auto-captioned you can either leave off the title attribute empty, or you can add "nocap" to the image's class attribute. The "nocap" control allows you to give the IMG a title without it being captioned.
You can set the Restrict Captioning option in the AutoCap Admin panel. After that only images with an "autocap" class attribute will be captioned. Note that the "autocap" attribute will be removed from the IMG by the plugin to prevent class name conflicts (if you want to use your own CSS you can always assume that "autocap" will be the DIV that wraps the output).