Every blogger add images in their blogs. Images are necessary to attract reader attention. But if image used in post in is too big they can break your blog layout. You can automatically adjust image size according to your content area.
Simply paste the following in your style.css file:

.post img {
max-width: 500px; /* Adjust this value according to your content area size*/
height: auto;
}


You can set your own max image size in code. Most WordPress themes display posts content within a <div> tag. However, if the hack don’t work, make sure you have this tag on your single.php file.