Image thumbnail size not updating in list

Hi, Can you pls. let me know when adding an image in page i already specified that it should create a thumbnail of size 100 but when previewing the list page the size is still the orginal large size of the image The value of image is coming from {$row.1Image_value} in list page and when i sa source code there was no mention of the width height of the image, only src of the image.
Does this creates thumbnails or NO ? Seems like yes as i see an extra th_image in my files folder but even that image of the same size as the orginal image.
So seems like in the creation of thumbnail is the problem ? or i m doing something wrong.
This is the coding of the list.asp where it was suppose to print with specific size.
value="<a target=_blank href=""" & my_htmlspecialchars(AddLinkPrefix("Logo",rs("Logo"),""))& """>"

value= value & "<img"

if thumbname=dbvalue(rs("Logo")) then

value=value & " width=100"

value=value & " height=150"

end if

value= value & " border=0"

value=value & " src=""" & my_htmlspecialchars(AddLinkPrefix("Logo",thumbname,"")) & """></a>"
Thanks for yr help.