I think the LoadPicture() function will look for a system file so you don't want that.
Add the pictures into images on a worksheet. This way they will be in the workbook.

Then right click the image you just added and select properties. Select picture property and navigate to your image file.

You can change the name to make sense of your pictures also. So they don't have to be Image1 Image2 etc.
Then in your code set the picture that you want to change = the image that you want.
If something
Image1.Picture = Image2.Picture
Else
Image1.Picture = Image3.Picture
End If
Here Image1 is the picture that changes based on what happens when the calculate button is pressed. Image3 is one of the images that you loaded into the workbook.
If you are going to store them on some other worksheet you may need to declare a worksheet object and set it to that sheet
Dim ws As Excel.Worksheet
Set ws = ActiveWorkbook.Sheets("ImageWorksheet")
Image1.Picture = ws.Image3.Picture
or something like this may work.
ActiveWorkbook.Sheets("ImageWorksheet").Image3.Picture
Something like that.