WordPress provides different sizes of images , the size of the uploaded image can be edited form Setting > Media and give the required value .But sometime we may need other sizes imaged too so for that purpose we can use the function.php of the theme for custom options. I found it from
http://buckleupstudios.com/blog/auto-resize-wordpress-featured-image-and-crop-if-necessary/
Just add
add_image_size($name, $width, $height, $cropBoolean);
For example : add_image_size('featuredImageCropped', 250, 200, true);