Seal / Protect Hand Tinted Aerial Photograph

[jtiii]

I have an old ~2'x3' photo that was made in the 1970's. The company that did it put a note on the back saying that it was painted with Marshal oil paints and protected by a Krylon finish. If you get right up on it, the whole surface has tiny cracks. My initial thought was a matte spray krylon but I'm worried about those cracks and also worried about getting an even coverage. What do you recommend?

 

[ProSignTN]

Too Late!! You can clear over, but unless it is thick enough to encapsulate the cracks and form a new first surface above.