Question Adding comment and author

[Zexor]

how do i add author , comment or rating into a jpg file?

 

[Zexor]

Exif

I guess its called EXIF. Those data are lost after i resize the image and save it.

 

[Pirahnaplant]

I couldn't find any code to do this, so I wrote some myself. I couldn't find out where the rating was stored in the files, so I didn't include it.

    Private Sub SetJpgProperty(ByVal filename As String, ByVal Prop As JpgProperty, ByVal value As String)
        Dim fs As New IO.BinaryReader(New IO.FileStream(filename, IO.FileMode.Open))
        'Advances the FileStream to the position of the property and saves it
        fs.BaseStream.Seek(&H30 + 12 * Prop, IO.SeekOrigin.Begin)
        Dim startPos As UInteger = fs.ReadUInt32 + 30
        fs.BaseStream.Seek(startPos, IO.SeekOrigin.Begin)
        'Advances the stream to the end of the property to record its length
        Do Until fs.ReadUInt16 = 0
        Loop
        Dim offsetLen As Integer = value.Length * 2 - CInt(fs.BaseStream.Position - startPos) + 2
        'Backs up the jpg image data for when we insert the property
        Dim jpgData(CInt(fs.BaseStream.Length - fs.BaseStream.Position - 1)) As Byte
        fs.Read(jpgData, 0, CInt(fs.BaseStream.Length - fs.BaseStream.Position))
        'Write new property data
        fs.BaseStream.Seek(startPos, IO.SeekOrigin.Begin)
        WriteString(fs.BaseStream, value)
        fs.BaseStream.WriteByte(0)
        fs.BaseStream.WriteByte(0)
        'Write the preserved data
        fs.BaseStream.Write(jpgData, 0, jpgData.Count)
        'Update property data length
        fs.BaseStream.Seek(&H2C + 12 * Prop, IO.SeekOrigin.Begin)
        WriteUInteger(fs.BaseStream, value.Length * 2 + 2)
        'Update data pointer
        fs.BaseStream.Seek(&H16, IO.SeekOrigin.Begin)
        IncUShortB(fs.BaseStream, offsetLen)
        'Update property pointers
        fs.BaseStream.Seek(&H30, IO.SeekOrigin.Begin)
        Dim v As UInteger
        For l As Integer = 0 To 4
            v = fs.ReadUInt32
            If v + 30 > startPos Then
                fs.BaseStream.Seek(-4, IO.SeekOrigin.Current)
                WriteUInteger(fs.BaseStream, v + offsetLen)
            End If
            fs.BaseStream.Seek(8, IO.SeekOrigin.Current)
        Next
        fs.Close()
    End Sub

    Private Sub WriteUInteger(ByVal fs As IO.Stream, ByVal value As UInteger)
        fs.WriteByte(CByte(value Mod &H100))
        fs.WriteByte(CByte(value \ &H100 Mod &H10000))
        fs.WriteByte(CByte(value \ &H10000 Mod &H1000000))
        fs.WriteByte(CByte(value \ &H1000000))
    End Sub

    Private Sub IncUShortB(ByVal fs As IO.Stream, ByVal value As Integer)
        Dim v As UShort = fs.ReadByte() * 256
        v += fs.ReadByte
        v += value
        fs.Seek(-2, IO.SeekOrigin.Current)
        fs.WriteByte(CByte(v \ &H100))
        fs.WriteByte(CByte(v Mod &H100))
    End Sub

    Private Sub WriteString(ByVal fs As IO.Stream, ByVal str As String)
        For l As Integer = 0 To str.Length - 1
            Dim v As Integer = Asc(str.Chars(l))
            If v < &H100 Then
                fs.WriteByte(CByte(v Mod &H100))
                fs.WriteByte(0)
            Else
                fs.WriteByte(CByte(v Mod &H100))
                fs.WriteByte(CByte(v Mod &H10000 \ &H100))
            End If
        Next
    End Sub

    Private Enum JpgProperty
        Title = 0
        Comments = 1
        Author = 2
        Keywords = 3
        Subject = 4
    End Enum

If you could provide me a couple copies of a file with different ratings, I could probably find where it's stored.

Edit: it doesn't work when the set string is 0 or 1 characters, I'll fix it soon.

Edit2: I found another problem, it can only modify existing properties, if the image doesn't contain a property, then the program crashes. I am completely lost on how to fix this, so I may not be able to get it to work.
But I did find a web site that sounds like it might be what you're looking for. I haven't tested it, but I suggest you take a look: Discovering the properties of an image.
Or this: CodeProject: Photo Properties. Free source code and programming help

 

[Zexor]

Thanks, i will try it. Does this class works? CodeProject: The ExifWorks class. Free source code and programming help It seem to be able to read some of the prop but missing some other ones.

I tried your code but it seem to get an overflow error in WriteUInteger. I try writing an author to a file that already has author in it.