<form method="post" enctype="multipart/form-data">
            <label for="cheval">Cheval :</label>    
            <input type="file" name="image" />
            <input type="submit" value="Modifier" />
          </form>

        <?php
        if(isset($_POST["submit"])) 
        {
            $dos = $_SERVER['DOCUMENT_ROOT']."/poney/img/";
            $image = $dos.$_FILES["image"]["name"];
            simpleName($image);
            $uploadOk = 1;
            $type = strtolower(pathinfo($image,PATHINFO_EXTENSION));

            $check = getimagesize($_FILES["image"]["tmp_name"]);
            if($check !== false) 
            {
                echo " Image - " . $check["mime"] . ".";
                $uploadOk = 1;
            } 
            else 
            {
                echo " Ce n'est pas une image.";
                $uploadOk = 0;
            }
            if (file_exists($image)) 
            {
                echo " Cette image existe déjà.";
                $uploadOk = 0;
            }
            if ($_FILES["image"]["size"] > 5000000) 
            {
                echo " Image trop grande";
                $uploadOk = 0;
            }
            if($type != "jpg" && $type != "png" && $type != "jpeg") 
            {
                echo " Seulement les images de type JPG, PNG et JPEG sont autorisées.";
                $uploadOk = 0;
            }
            if ($uploadOk == 0) 
            {
                echo " Image non téléchargée";
            }
            if (move_uploaded_file($_FILES["image"]["tmp_name"], $image))
            {               
                $sql = 'UPDATE cheval_nom SET image = "'.$_FILES["image"]["name"].'" WHERE id = '.$_GET['id'];
                $req = $bdd->prepare($sql);
                $req->execute();
            }
            else
            {
                echo "Erreur dans le téléchargement de l'image !";
            } 
        } 

<form method="post" enctype="multipart/form-data">
            <label for="cheval">Cheval :</label>    
            <input type="file" name="image" />
            <input type="submit" value="Modifier" />
        </form>
        <?php
        $dos = $_SERVER['DOCUMENT_ROOT']."/poney/img/";
        $image = $dos . basename($_FILES["image"]["name"]);
        $image = strtr($image,'ÀÁÂÃÄÅÇÈÉÊËÌÍÎÏÒÓÔÕÖÙÚÛÜÝàáâãäåçèéêëìíîïðòóôõöùúûüýÿ','AAAAAACEEEEIIIIOOOOOUUUUYaaaaaaceeeeiiiioooooouuuuyy');
        $uploadOk = 1;
        $type = strtolower(pathinfo($image,PATHINFO_EXTENSION));

        if(isset($_POST["submit"])) 
        {
            $check = getimagesize($_FILES["image"]["tmp_name"]);
            if($check !== false) 
            {
                echo "Image - " . $check["mime"] . ".";
                $uploadOk = 1;
            } 
            else 
            {
                echo "Ce n'est pas une image.";
                $uploadOk = 0;
            }
        }
        if (file_exists($image)) 
        {
            echo "Cette image existe déjà.";
            $uploadOk = 0;
        }
        if ($_FILES["image"]["size"] > 5000000) 
        {
            echo "Image trop grande";
            $uploadOk = 0;
        }
        if($type != "jpg" && $type != "png" && $type != "jpeg") 
        {
            echo "Seulement les images de type JPG, PNG et JPEG sont autorisées.";
            $uploadOk = 0;
        }
        if ($uploadOk == 0) 
        {
            echo "Image non téléchargée";
        } 
        else 
        {
            if (move_uploaded_file($_FILES["image"]["tmp_name"], $image))
            {
                ?>
                <img src="/poney/img/<?php echo $_FILES["image"]["name"]?>"/><?php
            } 
            else 
            {
                echo "Erreur dans le téléchargement de l'image.";
            }
        }
        ?>

<form method="post" action="img.php" enctype="multipart/form-data">
    <label for="cheval">Cheval</label>
    <img src=""/>
    <input type="file" name="image" />
</form>

<?php
header ("Content-type: image/jpeg");
 
if (isset($_FILES['image']))
{
   
}
?>