I know this might be a little obvious, but is the original image in JPEG format? Check the file extension of the original saved photo. Some photo programs will save the file format in the default set by the app. This may be causing the confusion.
What I would suggest is open the image/photo in a graphics editor, such as Paint if you don't have anything more advanced.
Once opened, select File > Save as
Select the directory you wish to save the file.
In the save option, select JPEG File Interchange Format from the available file types.
Once selected, give the file a name and click Save.
Now try attaching the new image into an email and send.