Here is some basic code to resize an image upon upload. Since many of us don't want our users uploading HUGE files, we can constrain the size, width and height. This is pretty straight forward. Example is written in VB.
 
For starters, this code goes in your page behind file (yourpage.aspx.vb) ...
***Replace YOUR_IMAGE_FIELD_NAME with the name of your own image upload field***

 

Public Sub SaveButton_Click(ByVal sender As Object, ByVal args As EventArgs)

' Click handler for SaveButton.

' Customize by adding code before the call or replace the call to the Base function with your own code.

If Not YOUR_IMAGE_FIELD_NAME.HasFile Then

SaveButton_Click_Base(sender, args)

Else

If YOUR_IMAGE_FIELD_NAME.HasFile Then

Dim filepath As String = YOUR_IMAGE_FIELD_NAME.PostedFile.FileName

Dim fileExt As String = LCase(System.IO.Path.GetExtension(YOUR_IMAGE_FIELD_NAME.FileName))

Dim myUpload As HttpPostedFile = YOUR_IMAGE_FIELD_NAME.PostedFile

If (fileExt = ".gif" Or fileExt = ".jpg" Or fileExt = ".bmp") And YOUR_IMAGE_FIELD_NAME.PostedFile.ContentLength < 500000 Then

Try

SaveButton_Click_Base(sender, args)

Catch ex As Exception

YOUR_IMAGE_FIELD_NAME_Label.Text = "ERROR: " & ex.Message.ToString() & ""

End Try

Else

YOUR_IMAGE_FIELD_NAME_Label.Text = "Only .gif, .jpg or .bmp files are allowed!

Also, images must be less than 500kb."

End If

End If

End If

' NOTE: If the Base function redirects to another page, any code here will not be executed.

End Sub

 

'This is where we resize the uploaded image before saving to the database

Public Overrides Sub GetUIdata()

MyBase.GetUIData() ' this calls the base apply of the user data 

Const bmpW As Integer = 300 'New image target width

Const bmpH As Integer = 325 'New Image target height 

If YOUR_IMAGE_FIELD_NAME.HasFile Then

Dim newWidth As Integer = bmpW

Dim newHeight As Integer = bmpH

Dim Pic() As Byte = Me.DataSource.YOUR_IMAGE_FIELD_NAME

' Convert to image for resizing

Dim Img As Bitmap = Nothing

Img = CType(Bitmap.FromStream(New MemoryStream(Pic, 0, Pic.Length - 1)), Drawing.Bitmap)

Dim newImg As Bitmap = New Bitmap(newWidth, newHeight, Imaging.PixelFormat.Format24bppRgb)

newImg.SetResolution(72, 72)

'Get the uploaded image width and height 

Dim upWidth As Integer = Img.Width

Dim upHeight As Integer = Img.Height

Dim newX As Integer = 0 'Set the new top left drawing position on the image canvas

Dim newY As Integer = 0

Dim reDuce As Decimal

'Keep the aspect ratio of image the same if not 4:3 and work out the newX and newY positions 

'to ensure the image is always in the center of the canvas vertically and horizontally 

If upWidth > upHeight Then 'Landscape picture 

reDuce = CDec(newWidth / upWidth)

'calculate the width percentage reduction as decimal 

newHeight = CInt(Int(upHeight * reDuce))

'reduce the uploaded image height by the reduce amount 

newY = CInt(Int((bmpH - newHeight) / 2))

'Position the image centrally down the canvas 

newX = 0 'Picture will be full width 

ElseIf upWidth < upHeight Then 'Portrait picture 

reDuce = CDec(newHeight / upHeight)

'calculate the height percentage reduction as decimal 

newWidth = CInt(Int(upWidth * reDuce))

'reduce the uploaded image height by the reduce amount 

newX = CInt(Int((bmpW - newWidth) / 2))

'Position the image centrally across the canvas 

newY = 0 'Picture will be full hieght 

ElseIf upWidth = upHeight Then 'square picture 

reDuce = CDec(newHeight / upHeight)

'calculate the height percentage reduction as decimal 

newWidth = CInt(Int(upWidth * reDuce))

'reduce the uploaded image height by the reduce amount 

newX = CInt(Int((bmpW - newWidth) / 2)) 'Position the image centrally across the canvas 

newY = CInt(Int((bmpH - newHeight) / 2)) 'Position the image centrally down the canvas 

End If

'Create a new image from the uploaded picture using the Graphics class 

'Clear the graphic and set the background color to white 

'Use Antialias and High Quality Bicubic to maintain a good quality picture 

'Save the new bitmap image using 'jpg' picture format and the calculated canvas positioning 

Dim newGraphic As Graphics = Graphics.FromImage(newImg)

newGraphic.Clear(Color.White)

newGraphic.SmoothingMode = Drawing2D.SmoothingMode.AntiAlias

newGraphic.InterpolationMode = Drawing2D.InterpolationMode.HighQualityBicubic

newGraphic.DrawImage(Img, newX, newY, newWidth, newHeight)

Dim stream As MemoryStream = New MemoryStream

newImg.Save(stream, System.Drawing.Imaging.ImageFormat.Jpeg)

Me.DataSource.YOUR_IMAGE_FIELD_NAME = stream.ToArray ' assign back to picture

stream.Close()

Img.Dispose()

newImg.Dispose()

newGraphic.Dispose()

End If

Do you a C# sample for resize image before uploading a image.

Thanks, will test it.