Imports GrapeCity.Documents.Excel
Imports System.Drawing

・・・

Sub Main()
　　Dim book As New Workbook
　　Dim sheet As IWorksheet = book.ActiveSheet
　　Dim cell As IRange = sheet.Range("B3")
　　Dim rect As Rectangle = GetCellPosition(sheet, cell)

　　sheet.Shapes.AddPictureInPixel("DioDocs_Mark.png", rect.X, rect.Y, rect.Width, rect.Height)
　　book.Save("Test.xlsx")
End Sub

Private Function GetCellPosition(ByVal sheet As IWorksheet, ByVal cell As IRange) As Rectangle
　　Dim cellLeft As Integer = cell.Column
　　Dim cellTop As Integer = cell.Row
　　Dim result As Rectangle = New Rectangle()

　　result.Width = CInt(sheet.Columns(cellLeft).ColumnWidthInPixel)
　　result.Height = CInt(sheet.Rows(cellTop).RowHeightInPixel)

　　For colIndex As Integer = 0 To cellLeft - 1
　　　　result.X += CInt(sheet.Columns(colIndex).ColumnWidthInPixel)
　　Next

　　For rowIndex As Integer = 0 To cellTop - 1
　　　　result.Y += CInt(sheet.Rows(rowIndex).RowHeightInPixel)
　　Next

　　Return result
End Function

using GrapeCity.Documents.Excel;
using System.Drawing;

・・・

static void Main()
{
　　var book = new Workbook();
　　var sheet = book.ActiveSheet;
　　var cell = sheet.Range["B3"];
　　var rect = GetCellPosition(sheet, cell);

　　sheet.Shapes.AddPictureInPixel("DioDocs_Mark.png", rect.X, rect.Y,rect.Width, rect.Height);
　　book.Save("Test.xlsx");
}

static Rectangle GetCellPosition(IWorksheet sheet, IRange cell)
{
　　int cellLeft = cell.Column;
　　int cellTop = cell.Row;
　　Rectangle result = new Rectangle();

　　result.Width = (int)sheet.Columns[cellLeft].ColumnWidthInPixel;
　　result.Height = (int)sheet.Rows[cellTop].RowHeightInPixel;

　　for (int colIndex = 0; colIndex < cellLeft; colIndex++)
　　　　result.X += (int)sheet.Columns[colIndex].ColumnWidthInPixel;
　　for (int rowIndex = 0; rowIndex < cellTop; rowIndex++)
　　　　result.Y += (int)sheet.Rows[rowIndex].RowHeightInPixel;

　　return result;
}