rasgele resimde "alt" sekmesi nasıl yapılır

<script language="JavaScript" type="text/javascript">
today=new Date();
jran=today.getTime();
function rnd() {
ia=9301;
ic=49297;
im=233280;
jran = (jran*ia+ic) % im;
return jran/(im*1.0);
};
function rand(number) {
return Math.ceil(rnd()*number);
};
document.write("<CENTER>");
for(i=1;i<=1;i++) {
myNum=(rand(12));
if(myNum == 1) document.write("<img src='/1.jpg'>"); 
if(myNum == 2) document.write("<img src='/2.jpg'>");
if(myNum == 3) document.write("<img src='/3.jpg'>"); 
if(myNum == 4) document.write("<img src='/4.gif'>"); 
if(myNum == 5) document.write("<img src='/5.gif'>");
if(myNum == 6) document.write("<img src='/6.gif'>"); 
if(myNum == 7) document.write("<img src='/7.gif'>"); 
if(myNum == 8) document.write("<img src='/8.gif'>");
if(myNum == 9) document.write("<img src='/9.jpg'>"); 
if(myNum == 10) document.write("<img src='/10.jpg'>"); 
if(myNum == 11) document.write("<img src='/11.jpg'>");
if(myNum == 12) document.write("<img src='/13.jpg'>"); 

else {
document.write();
}
};
document.write("</CENTER>");
</script>

<script language="JavaScript" type="text/javascript">
today=new Date();
jran=today.getTime();
function rnd() {
ia=9301;
ic=49297;
im=233280;
jran = (jran*ia+ic) % im;
return jran/(im*1.0);
};
function rand(number) {
return Math.ceil(rnd()*number);
};
document.write("<CENTER>");
for(i=1;i<=1;i++) {
myNum=(rand(12));
if(myNum == 1) document.write("<img src='/1.jpg' alt='demo23' width='100' height='100' >"); 
if(myNum == 2) document.write("<img src='/2.jpg' alt='demoef' width='100' height='100' >");
if(myNum == 3) document.write("<img src='/3.jpg' alt='demodfghfh' width='100' height='100' >"); 
if(myNum == 4) document.write("<img src='/4.gif' alt='demo6776' width='100' height='100' >"); 
if(myNum == 5) document.write("<img src='/5.gif' alt='demtrfhgo' width='100' height='100' >");
if(myNum == 6) document.write("<img src='/6.gif' alt='demo676767' width='100' height='100' >"); 
if(myNum == 7) document.write("<img src='/7.gif' alt='demohg' width='100' height='100' >"); 
if(myNum == 8) document.write("<img src='/8.gif' alt='demo87867' width='100' height='100' >");
if(myNum == 9) document.write("<img src='/9.jpg' alt='demo5656yry' width='100' height='100' >"); 
if(myNum == 10) document.write("<img src='/10.jpg' alt='demogjhhj hjhtr' width='100' height='100' >"); 
if(myNum == 11) document.write("<img src='/11.jpg' alt='dem   hgh ' width='100' height='100' >");
if(myNum == 12) document.write("<img src='/13.jpg' alt='demog gh  gh' width='100' height='100' >"); 

else {
document.write();
}
};
document.write("</CENTER>");
</script>

<script language="JavaScript" type="text/javascript">
<!--
today=new Date();
jran=today.getTime();
function rnd() {
ia=9301;
ic=49297;
im=233280;
jran = (jran*ia+ic) % im;
return jran/(im*1.0);
};
function rand(number) {
return Math.ceil(rnd()*number);
};
document.write("<CENTER>");
myNum=(rand(12));
switch(myNum)
{
 case 1: resim = "'/1.jpg' alt='demo23' width='100' height='100'"; 
 case 2: resim = "'/2.jpg' alt='demoef' width='100' height='100'";
 case 3: resim = "'/3.jpg' alt='demodfghfh' width='100' height='100'"; 
 case 4: resim = "'/4.gif' alt='demo6776' width='100' height='100'"; 
 case 5: resim = "'/5.gif' alt='demtrfhgo' width='100' height='100'";
 case 6: resim = "'/6.gif' alt='demo676767' width='100' height='100'"; 
 case 7: resim = "'/7.gif' alt='demohg' width='100' height='100'"; 
 case 8: resim = "'/8.gif' alt='demo87867' width='100' height='100'";
 case 9: resim = "'/9.jpg' alt='demo5656yry' width='100' height='100'"; 
 case 10: resim = "'/10.jpg' alt='demogjhhj hjhtr' width='100' height='100'"; 
 case 11: resim = "'/11.jpg' alt='dem   hgh ' width='100' height='100'";
 case 12: resim = "'/13.jpg' alt='demog gh  gh' width='100' height='100'"; 
 default: resim = "";
}
if(resim != "")
 document.write("<img src='" + resim + ">");
document.write("</CENTER>");
-->
</script>