Get Original Dimension Featured Image on the homepage

The second parameter for wp_get_attachment_image_src is $size.

$size
(string/array) (optional) Size of the image shown for an image attachment: either a string keyword (thumbnail, medium, large or full)
or a 2-item array representing width and height in pixels, e.g.
array(32,32). As of Version 2.5, this parameter does not affect the
size of media icons, which are always shown at their original size.

http://codex.wordpress.org/Function_Reference/wp_get_attachment_image_src

Per that Codex entry $size can take string values of “thumbnail, medium, large or full”. You need “full” to get the full size image, which ought to be the original.

It seems to me like you could save yourself a little bit of trouble with wp_get_attachment_image instead of wp_get_attachment_image_src