Если интересует именно флекс, а не гридон, то как то так:
<!DOCTYPE html>
<html lang="en">
<head>
<link rel="stylesheet" href="style.css">
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
</head>
<body>
<div class="photos-div">
<img src="img.jpg" alt="" width="260" height="500">
<img src="img2.jpg" alt="" width="400" height="500">
<div style="display: flex; flex-direction: column; ">
<img src="img3.jpg" alt="" height="244" width="260">
<img src="img4.jpg" alt=""height="244" width="260"></div>
</div>
</body>
</html>
*{
padding: 0;
margin: 0;
}
.photos-div{
display: flex;
flex-direction: row;
}
.photos-div img{
margin: 6px;
object-fit: cover;
}
