You can use http://fotoforensics.com to easily get meta data from a graphics file. It's recommended in Craig Ball's 2016 E-Discovery Workbook.
You simply select a file and click 'Upload File'. The harvested metadata will show among many, many other things, the device use to take the photo and the software used to edit it.
You'll also get specific information about how the file was edited in Photoshop: