Go to:
components\com_content\views\category\tmpl\blog_item.php
Go to Line:
<?php echo $this->item->introtext; ?>
And replace with this:
<?php
preg_match('/<img (.*?)>/', $this->item->introtext, $match);
echo "<div class='blogimagesjoomir'>".$match[0];
echo(strip_tags($this->item->introtext)."</div>");
?>
and add this css to template css:
.blogimagesjoomir img{ float:right; margin:10px;}
.blogimagesjoomir{ text-align:justify;}