<?php
 
function is_image_extension($name) {
     return preg_match('#\.(png|jpeg|jpg|gif|bmp|tiff|ico)$#', $name);
}
 
$arquivos = array("semext", "apple.doc", "foo.png", "apple.txt", "foo.png", "banana.jpg", "apple.txt");
 
usort($arquivos, function ($value) {
    return !is_image_extension($value);
});
 
foreach ($arquivos as $arq) {
    if (is_image_extension($arq)) { //Verifica se a extensão é imagem
        echo '<img src="../images/documentos/', $arq, '" />', PHP_EOL;
    }else{
        echo '<li>', $arq, '</li>', PHP_EOL;
    }
}

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