如何将上传的图像转换为JPG格式

试试这个：

<?php
$path = "uploads/";
$img = $_FILES['photoimg']['tmp_name'];
$dst = $path . $_FILES['photoimg']['name'];
if (($img_info = getimagesize($img)) === FALSE)
  die("Image not found or not an image");
$width = $img_info[0];
$height = $img_info[1];
switch ($img_info[2]) {
  case IMAGETYPE_GIF  : $src = imagecreatefromgif($img);  break;
  case IMAGETYPE_JPEG : $src = imagecreatefromjpeg($img); break;
  case IMAGETYPE_PNG  : $src = imagecreatefrompng($img);  break;
  default : die("Unknown filetype");
}
$tmp = imagecreatetruecolor($width, $height);
imagecopyresampled($tmp, $src, 0, 0, 0, 0, $width, $height, $width, $height);
imagejpeg($tmp, $dst.".jpg");
?>

确保安装了GD库并使用它来将gif或png转换为jpg，例如

    if ($_FILES["photoimg"]["type"] == "image/jpeg" || $_FILES["photoimg"]["type"] == "image/png" || $_FILES["photoimg"]["type"] == "image/gif" )
    {
      if ($_FILES["photoimg"]["type"] == "image/png" || $_FILES["photoimg"]["type"] == "image/gif" )
      {
       imagejpeg(imagecreatefromstring(file_get_contents($_FILES["photoimg"]["tmp_name"])), "converted.jpg");
       $actual_image_name = time().$session_id.".".$ext;
       move_uploaded_file("converted.jpg", $path.$actual_image_name);
      }
      else
      {
        $actual_image_name = time().$session_id.".".$ext;
        $tmp = $_FILES['photoimg']['tmp_name'];
        move_uploaded_file($tmp, $path.$actual_image_name);
      }
    }