Image sizes, positioning

I need to place an image in a table cell that expands or shrinks depending on the screen size. I tried it through a style sheet but the size doesn't change. I cannot just place the image in the cell as I need to put something else there.

Is there a way to:
Change the image size through a style sheet
Have two layers of images in the same cell

I'm not totally sure what you want, but can't you just use a percentage on the image;

Code:

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<img src="IMG.png" alt="" style="width:75%; height="50%;">

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And for the second question, do you mean overlaying one image on top of another? If so I think you can do it in a couple of ways. You can use position, but I'd probably just go with a background image:

Code:

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<img src="IMG.png" alt="" style="background:url('IMG2.png') top left no-repeat;">

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Haven't tested it but I think it should work.