What you need to do is point the imageurl tag (or src for straight up <img> ran at server), to point grab binary data from your server.
There are more than likely many articles on how to do this if you google for 'get resized image in asp.net' (here's a sample article http://aspnet.4guysfromrolla.com/articles/012203-1.aspx)
The above article uses a webpage to serve up the image, but that really is silly since you do not need all the overhead and processing a webpage requires. But they do it for simplicity sake.
The preferred method would be to identify a special extension in a url request that an HttpModule / Handler could intercept, and return a straight binary response, without the processing of creating a webpage just to return binary data.
If your website is not dependant on performance, you can certainly use the above article's method and it will not matter. On the other hand, if this site is used by many, you should go the HttpModule route.
Anyway, in a datalist, you can simply define this on your front-size aspx:
then, in your code-behind:
<asp:datalist id="_pictureDataList" runat="server">
<itemTemplate><img id="frontsideimage" runat="server"></itemTemplate>
private void DataList_ItemDataBound(System.Web.UI.WebControls.DataListItemDataBoundEventArgs e)
if (e.Item.ItemType == ListItemType.Item || e.Item.ItemType == ListItemType.AlternatingItem)
row = e.Item.DataItem as DataRowView;
image = e.Item.Controls.FindControl('frontsideimage');
image.src = row["imageurl"];