The valid tag types as defined in the TIFF Baseline 6.0 are:
- 1: BYTE
- 2: ASCII
- 3: SHORT
- 4: LONG
- 5: RATIONAL
- 6: SBYTE
- 7: UNDEFINED
- 8: SSHORT
- 9: SLONG
- 10: SRATIONAL
- 11: FLOAT
- 12: DOUBLE
With an Hexadecimal Editor (e.g. HxD) change the type of any tag to a non-valid value. Tag type is set in the bytes 2-3 of each IFD entry (tag).