//specify minimum size for uploaded images (including featured images)
add_filter('wp_handle_upload_prefilter','tc_handle_upload_prefilter');
function tc_handle_upload_prefilter($file)
{
$img=getimagesize($file['tmp_name']);
$minimum = array('width' => '300', 'height' => '300');
$width= $img[0];
$height =$img[1];
if ($width < $minimum['width'] )
return array("error"=>"Image dimensions are too small. Minimum width is {$minimum['width']}px. Uploaded image width is $width px");
elseif ($height < $minimum['height'])
return array("error"=>"Image dimensions are too small. Minimum height is {$minimum['height']}px. Uploaded image height is $height px");
else
return $file;
} Reference Links
https://wordpress.stackexchange.com/questions/28359/how-to-require-a-minimum-image-dimension-for-uploading
