hammered? tin picture

Would appreciate any thoughts on age of this picture. It is a picture of an older ship. Thank you.
https://drive.google.com/folderview?id=0BxrtWjVO3RSvdThCTVA4eGpiTnM&usp=sharing

 

Really hard to tell age on this. Popular for decades up into the 60s.

 

At the bottom there appears to be a squarish cartouche with some kind of mark which may tell something about it. Something on upper right edge too, looks like an "U."

 

Is it magnetic? What most people call "tin" is usually tinned mild steel.

 

Thank you all for sharing your knowledge. The marks are not clear in the picture, but I think are part of something that attaches the picture to the board. I will need to check on whether it is magnetic. I did not know it was a popular pastime.

 

Could be aluminum, was used by artists in places like Africa and probably many others. They wanted to make monotone, relief works and aluminum sheets were apparently an economical alternative to copper.

 

I agree with hobby kit and 1960s . I think every house had one of these , as well as the string art !

 

The technique is called "repoussé".

 

Also sold in Spain as souvenirs.