Some picture editors are very fussy in that the content of the file MUST match the extension type of the name.

Try IrfanView to open the files, it is less fussy, also it doesn't matter what the extension is for the file, in fact if the extension was misnamed it will not only open the picture anyway, it will tell you what it really is, and ask you if you want it to correct it (you don't have to).

Try IrfanView at Click Here