how to replace these simple if else PHP statements with a function?

How can i improve or replace these if else PHP statements to a function which can take on a file name variable for ( eg images/dogtypeX.jpg ) instead of hard-coding every single dog type? Thank you to your all PHP masters!

header('Content-type: image/jpg');
$dogtype = $_GET["dogtype"];
$dogname = $_GET["dogname"];

if($dogtype== "dogtype1")
{ $jpg_image = imagecreatefromjpeg('images/dogtype1.jpg');}
else if ($dogtype== "dogtype2")
{ $jpg_image = imagecreatefromjpeg('images/dogtype2.jpg');}
else if ($dogtype=="dogtype3") 
{ $jpg_image = imagecreatefromjpeg('images/dogtype3.jpg');}
else if ($dogtype=="dogtype4")
{ $jpg_image = imagecreatefromjpeg('images/dogtype4.jpg');}
else if ($dogtype=="dogtype5")
{ $jpg_image = imagecreatefromjpeg('images/dogtype5.jpg');}
imagettftext($jpg_image, $dogtype, $dogname);
imagejpeg($jpg_image);