Export Attachments using Python script to modify file name [ArcGIS Desktop 10.8.1]

I’m trying to export photo attachments from a railroad crossings dataset taken with ArcGIS Collector, and would like to customize the naming convention so that the file name contains the crossing number. I stumbled across a script from @Midavalo that accomplishes this, however the files exported are no longer JPEG format. I have almost no knowledge of Python.

Feature table:

Attachment table:

Modified script:

import arcpy, os
from collections import defaultdict

inFC = r'C:UsersDesktopscratchCustomExportAttachmentsCopyFeatures.gdbCrossings'
inTable = r'C:UsersDesktopscratchCustomExportAttachmentsCopyFeatures.gdbCrossings__ATTACH'
fileLocation = r'C:UsersDesktopscratchCustomExportAttachmentsAttachments'

# Get dictionary of ObjectID and associated field value
myFeatures = dict()
with arcpy.da.SearchCursor(inFC, ['OID@', 'CROSSING']) as cursor:
    for row in cursor:
        myFeatures[row[0]] = row[1]

# Create dictionary to count usage of the field value (to increment files)
valueUsage = defaultdict(int)

# Loop through attachments, incrementing field value usage, and using that
# increment value in the filename
with arcpy.da.SearchCursor(inTable, ['ATTACHMENTID', 'ATT_NAME', 'REL_OBJECTID']) as cursor:
    for row in cursor:
        if row[3] in myFeatures:
            attachment = row[0]
            fieldValue = myFeatures[row[3]] # Value of specified field in feature class
            valueUsage[fieldValue] += 1 # Increment value
            filename = "{0}_{1}".format(fieldValue, valueUsage[fieldValue]) # filename = FieldValue_1
            output = os.path.join(fileLocation, filename) # Create output filepath
            open(output, 'wb').write(attachment.tobytes()) # Output attachment to file

Output folder:

Why are the photo attachments exporting as "File" instead of JPEG, and how should I change the script in order to make this happen?