<?php $loop = 0; ?>
<?php if(have_posts()) : while(have_posts()) : the_post();?>
<?php $loop++; ?>
<?php if( $loop == 1) {
//Do action for large image
} elseif( $loop == 2 ) {
//Do action for big image
} elseif( $loop > 2 && $loop <= 5 ){
//Do action for middle image
} elseif( $loop > 5 ) {
//Do action for small image
}?>
<?php endwhile; endif;?>
