Du har forstået det korrekt. Det den skal tjekke er om der er indtastet noget i feltet "billede" i databasen. Hvis der er det, skal den vise <img src=\"$pic[0]\">, og hvis der ikke er indtastet noget i feltet billede, skal den ikke vise noget.
Hvordan vil du sætte det der if empty ind i denne kode:
$query = mysql_query("SELECT * FROM `upload` WHERE `id` = '". $_GET["id"] ."'") or die (mysql_error());
if(mysql_num_rows($query) == 1) {
$vis = mysql_fetch_array($query);
$pics = "$vis[billede]";
$pic = explode(",", $pics);
$tekst = str_replace("\n","<br>\n",$vis[tekst]);
echo"
<table width=489 border=0>
<tr>
<td width=313 valign=top><table width=100 border=0 cellpadding=0 cellspacing=1 bgcolor=#000000>
<tr>
<td bgcolor=#E7E4E0> <p>$pic[0] width=\"270\">
</p></td>
</tr>
</table>
<font color=#000000 size=1 face=Verdana, Arial, Helvetica, sans-serif><br>
</font> <table width=240 border=0>
<tr>
<td width=154><table width=150 border=0 cellpadding=0 cellspacing=0>
<tr>
<td width=81><table width=69 border=0 cellpadding=0 cellspacing=1 bgcolor=#000000>
<tr>
<td width=133 bgcolor=#E7E4E0>
<a href=\"
http://www.biga-aarhus.dk/pass/upload/$pic[1]\" target=\"_blank\"><img src=\"../pass/upload/$pic[1]\" alt=\"$vis[navn] - $vis[sort]\" width=\"67\" height=\"50\" border=\"0\"></a></td>
</tr>
</table></td>
<td width=69><table width=69 border=0 cellpadding=0 cellspacing=1 bgcolor=#000000>
<tr>
<td width=133 bgcolor=#E7E4E0><a href=\"
http://www.biga-aarhus.dk/pass/upload/$pic[2]\" target=\"_blank\"><img src=\"../pass/upload/$pic[2]\" alt=\"$row[navn] - $row[sort]\" width=\"67\" height=\"50\" border=\"0\"></a></td>
</tr>
</table></td>
</tr>
</table></td>
<td width=76><table width=69 border=0 cellpadding=0 cellspacing=1 bgcolor=#000000>
<tr>
<td width=133 bgcolor=#E7E4E0><a href=\"
http://www.biga-aarhus.dk/pass/upload/$pic[3]\" target=\"_blank\"><img src=\"../pass/upload/$pic[3]\" alt=\"$row[navn] - $row[sort]\" width=\"67\" height=\"50\" border=\"0\"></a></td>
</tr>
</table></td>
</tr>
</table>
<font color=#000000 size=1 face=Verdana, Arial, Helvetica, sans-serif> <br>
Klik på billederne for at se dem i stor format </font></td>
<td width=166 valign=top><table width=196 border=0>
<tr>
<td colspan=2><font size=1 face=Verdana, Arial, Helvetica, sans-serif><strong>Udstillingskøkken</strong></font></td>
</tr>
<tr>
<td width=76><font size=1><strong><font color=#000000 face=Verdana, Arial, Helvetica, sans-serif>Navn:</font></strong></font></td>
<td width=110><font color=#000000 size=1 face=Verdana, Arial, Helvetica, sans-serif>$vis[navn]</font></td>
</tr>
<tr>
<td><font size=1><strong><font color=#000000 face=Verdana, Arial, Helvetica, sans-serif>Træsort:</font></strong></font></td>
<td><font color=#000000 size=1 face=Verdana, Arial, Helvetica, sans-serif>$vis[sort]</font></td>
</tr>
<tr>
<td><font face=verdana size=1 color=#000000><strong><font color=#000000 face=Verdana, Arial, Helvetica, sans-serif>Før
pris:</font></strong></font></td>
<td><font color=#000000 size=1 face=Verdana, Arial, Helvetica, sans-serif>$vis[before]</font></td>
</tr>
<tr>
<td><font face=verdana size=1 color=#000000><strong><font color=#000000 face=Verdana, Arial, Helvetica, sans-serif>Nu
pris:</font></strong></font></td>
<td><font color=#000000 size=1 face=Verdana, Arial, Helvetica, sans-serif>$vis[nu]</font></td>
</tr>
<tr>
<td><strong><font color=#000000 size=1 face=Verdana, Arial, Helvetica, sans-serif>Du
sparer:</font></strong></td>
<td><font color=#000000 size=1 face=Verdana, Arial, Helvetica, sans-serif>$vis[sparer]</font></td>
</tr>
</table>
<p><font face=verdana size=1 color=#000000>$tekst</font></strong></p>
</td>
</tr>
</table>
<font color=#000000 size=1 face=Verdana, Arial, Helvetica, sans-serif><br>
<a href=../tilbud.php target=_self>Tilbage</a></font>
";