Cropping and combining two images on server
Expanding on my comment above, I'd also follow Microsoft's naming guidelines and have the method names be PascalCased. Plus, I'm not a huge fan of mutable structs, preferring to initialize them via provided constructors. So I came up with the following:

public static class ImageCombiner
{
    private static readonly EncoderParameters encoderParameters = new EncoderParameters(1);

    private static readonly RectangleF sizeLocation1 = new RectangleF(0.0F, 0.0F, 400.0F, 400.0F);

    private static readonly RectangleF sizeLocation2 = new RectangleF(400.0F, 0.0F, 400.0F, 400.0F);

    private static readonly ImageCodecInfo jpgDecoder = ImageCodecInfo.GetImageDecoders().Single(codec =&gt; codec.FormatID == ImageFormat.Jpeg.Guid);

    private static readonly byte[] emptyImage = new byte[0];

    static ImageCombiner()
    {
        encoderParameters.Param[0] = new EncoderParameter(Encoder.Quality, 90L);
    }

    // Crops two squares out of two separate images
    // And then combines them into single image that's returned as byte[]
    public static byte[] CombineImages(IList&lt;HttpPostedFileBase&gt; itemPayload)
    {
        try
        {
            using (var ms = new MemoryStream())
            using (var bitmap = new Bitmap(800, 400, PixelFormat.Format24bppRgb))
            using (var img1 = Image.FromStream(itemPayload[0].InputStream))
            using (var img2 = Image.FromStream(itemPayload[1].InputStream))
            using (var g = Graphics.FromImage(bitmap))
            {
                g.DrawImage(img1, sizeLocation1, GetCropParams(img1), GraphicsUnit.Pixel);
                g.DrawImage(img2, sizeLocation2, GetCropParams(img2), GraphicsUnit.Pixel);
                bitmap.Save(ms, jpgDecoder, encoderParameters);
                return ms.ToArray();
            }
        }
        catch
        {
            return emptyImage;
        }
    }

    private static RectangleF GetCropParams(Image img)
    {
        return img.Width &gt; img.Height
            ? new RectangleF(
                    (img.Width / 2) - (img.Height / 2),
                    0.0F,
                    2 * (img.Height / 2),
                    img.Height)
            : new RectangleF(
                    0.0F,
                    (img.Height / 2) - (img.Width / 2),
                    img.Width,
                    2 * (img.Width / 2));
    }
}