I don't know enough about Publisher mail merges to know if this is possible without coding so I would use a macro to output jpg files.
Code:
Sub TestExport()
Dim sName As String, sPath As String
With ActiveDocument.MailMerge.DataSource
.ActiveRecord = 1
Do
sName = .DataFields.Item("Name").Value
sPath = .DataFields.Item("JpgFolderPath").Value & "\" & .DataFields.Item("JpgFileName").Value
ActiveDocument.Pages(1).SaveAsPicture Filename:=sPath, pbResolution:=pbPictureResolutionWeb_96dpi
If .ActiveRecord = .RecordCount Then Exit Do
.ActiveRecord = .ActiveRecord + 1
Loop
End With
End Sub