Store all your pictures in a folder on your hard drive.
In your table, store just the picture name and it's extension (i.e.
AuntTillie.jpg)  in a regular text field named [PictureName].

Add an Image control to the form (in the Detail Section?)
Note: You'll need to select any image picture to get the control to
'stick'. Then delete the control's picture property. When prompted
click OK. When done the Image Picture property should read (none).

Code the Form's Current event:
If Not IsNull([PictureName]) Then
      Me!ImageName.Picture = "c:\folderpath\" & [PictureName]
      Me![ImageName].Visible = True
Else
    Me!ImageName].Visible = False
End If

If the pictures are stored in various different folders, then include
the path to the folder in with the [PictureName] field in the table.
Change the above code from:
Me!ImageName.Picture = "c:\folderpath\" & [PictureName]
to
Me!ImageName.Picture =  [PictureName]