Is it the painting of Emperor Jiaqing or is it a painting painted by Emperor Jiaqing himself?
If it’s the former, it depends on who painted it and when.
If it is the latter, it must be very valuable. Donate to a museum. Let's take a look too.
By the way, Emperor Jiaqing wrote very well and was one of the four major calligraphers in China at that time. I just don’t know what his paintings are like.