Adding Images triggers "ResourceWarning: unclosed file"

Doing a basic test with Warnings enabled

import openpyxl

wb = openpyxl.Workbook()
ws = wb.worksheets[0]
img = openpyxl.drawing.image.Image('test.jpg')
img.anchor = 'A1'
ws.add_image(img)
wb.save('out.xlsx')

Triggers

ResourceWarning: unclosed file <_io.BufferedReader name='test.jpg'> (openpyxl.writer.excel:116) .../site-packages/openpyxl/writer/excel.py

The fix is pretty simple - Provide access and I'll give you a pull request.