I found an interesting painting

Years ago I purchased a painting at a garage sale. The sale was at the home of an eighty year old woman who had recently died and her kids were selling off some of the items.

I purchased a pencil drawing done by a local businessman who had died a few years earlier. I'm assuming he had signed the sketch for this woman and she placed it in the frame.

The reason I bought it was because the frame was obviously quite old and on the back, on very old cardboard was a tag which read...

Carman Studio, Inc.
Antiques
1513 Wisconsin Avenue N.W.
Washington 7 D.C.

I thought there might be another painting underneath, so I paid the two dollars and took the painting home. I never did get around to looking behind the print, until today.

I was correct -- there was another painting behind the sketch.

It is a painting of a military operation with these words in block letter printed beneath the painting...

LANDING OF THE AMERICAN FORCES UNDER GENERAL SCOTT

AT VERA CRUZ

MARCH 9TH 1847

What do you suppose I have here, if anything? Where might a person have this appraised? Or would that be a waste of time?