Propozycja. Ja bym zrezygnował z tag-u <p> (tag-ów) na rzecz jednego np.: <div> jako "kontenera" dla obrazków.
Dodatkowo użyłem: Figure i Figcaption
<!DOCTYPE html>
<html lang="pl">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Passerwis</title>
<link href="https://fonts.googleapis.com/css?family=Roboto:400,900&subset=latin-ext">
<link href="favicon.ico" rel="shortcut icon" type="image/x-icon" >
<link rel=stylesheet href="style.css">
</head>
<body>
<div id="wrapper">
<header>
<img />
</header>
<nav>
<a class="menu" href="#">Oferta</a>
<a class="menu" href="#">O nas</a>
<a class="menu" href="#">Kontakt</a>
</nav>
<section>
<article>
<h1>Passerwis</h1>
<div class="images-container">
<figure>
<img id="big-1" src="eseb logo.jpg" alt="eseb logo - header" />
<figcaption>Tu napis</figcaption>
</figure>
<figure>
<img id="big-2" src="kemppi logo.jpg" alt="kemppi logo.jpg - header" />
<figcaption>Tu napis</figcaption>
</figure>
<figure>
<img id="big-3" src="lincoln logo.jpg" alt="lincoln logo.jpg - header" />
<figcaption>Tu napis</figcaption>
</figure>
<figure>
<img id="big-4" src="bester logo.jpg" alt="bester logo.jpg - header" />
<figcaption>Tu napis</figcaption>
</figure>
</div>
</article>
<iframe src="https://www.google.com/maps/embed?pb=!1m18!1m12!1m3!1d2459.584339558667!2d15.488347851718606!3d51.94153487960923!2m3!1f0!2f0!3f0!3m2!1i1024!2i768!4f13.1!3m3!1m2!1s0x470613e4a2233603%3A0xfac2d1385c066691!2sPAS%20SERWIS!5e0!3m2!1spl!2spl!4v1619808202997!5m2!1spl!2spl" width="600" height="450" style="border:0;" allowfullscreen="" loading="lazy"></iframe>
</section>
<footer></footer>
</div>
</body>
</html>
* {
margin: 0;
padding: 0;
font-family: Roboto, -apple-system, BlinkMacSystemFont,
'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, 'Open Sans',
'Helvetica Neue', sans-serif;
box-sizing: border-box;
}
body {
background-color: grey;
}
#wrapper {
max-width: 1000px;
margin: 0 auto;
background-color: grey;
}
header img {
max-width: 100%;
display: block;
}
nav {
background-color: black;
}
a.menu {
display: inline-block;
width: 25%;
padding: 45px 60px;
color: white;
text-decoration: none;
text-align: center;
}
a.menu:hover {
background-color: grey;
}
h1 {
text-align: center;
}
.images-container {
text-align: center;
margin: 1em 0;
}
.images-container figure {
display: inline-block;
}
.images-container figcaption {
padding: 0.5em 0;
font-family: Arial;
font-weight: bold;
color: white;
background-color: rgba(0,0,0,0.2);
margin: 0 1em;
}
.images-container img {
max-width: 150px;
max-height: 100px;
margin: 1em;
}