DD-Block resizes images
ddblock-processed class is added to your div when the Javascript event is attached to it by Drupal. This is normal behavior, but it shouldn't be too hard to override the style with CSS.

To show you a simple example of CSS overrides (even though this is considered an inefficient selector, it doesn't matter too much in cases such as yours):

If on the original style, the CSS is declared as follows:

.ddblock-processed {
  width: 100px;
}


You can easily override it in your own stylesheet by including the "parent" element in the CSS selector. So if ddblock-processed div's parent is a div with an ID of myregion then doing this will override it:

div.ddblock-processed {
  width: 200px;
}

/* OR */

#myregion .ddblock-processed {
  width: 200px;
}

/* OR */

body .ddblock-processed {
  width: 200px;
}

/* OR */

div .ddblock-processed {
  width: 200px;
}


This is called CSS specificity if you want to read up about it.