Sorry for not updating this post earlier, as we've resolved this issue a bit later.
We use RadGrid with GridBinaryImageColumn to upload JPG images (back-end).
We show these images (front-end) using a repeater and RadBinaryImage.
Displaying these as they are fed directly from the database results in huge BMP images.
Problem was resolved by processing the images before displaying them:
DataValue='<%# FormatImage(Eval("ArtImage")) %>' ResizeMode="None"
AlternateText='<%# Eval("ArtTitle") %>' ToolTip='<%# Eval("ArtTitle") %>' runat="server" />
And in the codeBehind (VB.NET):
Public Function FormatImage(ByVal img As Byte()) As Byte()
Dim stream As New MemoryStream(img)
Dim streamOut As New MemoryStream
Dim myImage As Image = Image.FromStream(stream)
This displays as a JPG image (with reduced weight).