You have the 25¢ Niagara Falls from the years 1922-30. It is a somewhat common stamp and is worth no more than a dollar or two if used.

To determine the difference the two varieties of the 25¢ Niagara Falls one needs to look at the perforations. You will need a copy of the very common 1932 3¢ Washington (#720). A picture of which is shown below. Follow the instructions below

The value of #568 can be found by clicking here.
The value of #699 can be found by clicking here.

There is another way of determining the difference between #568 and #699, that is to look at the type of printing. #699 was printed using the Rotary Press Printing which makes the stamp wider and longer than #568 which was printed using the Flat Plate Printing method. An illustration of the degree of difference between the two printings is shown below;

Lastly #568 tends towards yellow green whilst #699 tends towards blue green.