Never mind i found this code that did the trick.
/* BEGIN Image resize */
#posts IMG
{
max-width: 700px;
width: expression (this.width > 700 ? "700px" : true);
}
#collapseobj_threadreview IMG {
max-width: 700px;
width: expression(this.width > 700 ? 700: true);
}
/* END Image resize */
Simply put this piece of code into "Additional CSS Definitions" under Style Manager -> Main CSS of the template you want this mod apply to.