done this recently for our new allpay install in the dining room. It all worked as described by @vikpaw except bulk rename utility which i took one look at and then decided I didn't have time to figure out that crazy program. Also the site itself was incredibly slow.
I wrote my own vbs script in 30mins.
Const ForReading = 1, ForWriting = 2, ForAppending = 8
Const TristateUseDefault = -2, TristateTrue = -1, TristateFalse = 0
Dim fso, f, ts,strpath
Set fso = CreateObject("Scripting.FileSystemObject")
Set f = fso.GetFile("upns.csv")
Set FLD = FSO.GetFolder(strPath)
Set ts = f.OpenAsTextStream(ForReading, TristateUseDefault)
Do While ts.AtEndOfStream <> True
TextStreamTest = split(ts.ReadLine,",")
For Each fil in FLD.Files
strOldNamearray = split(fil.Path,"\")
fname = strOldNamearray(2)
matchname = adno & ".jpg"
newname = strpath & "\" & upn & ".jpg"
if fname = matchname then fso.movefile fil.path, newname
set fso = nothing
set fld = nothing