One way, though the resolution won't be quite perfect on the copies, is to have the picture be located on one page, and have the pictures on the other 6 pages be linked to *the cell(s) containing* the picture.
You can try it out as follows:
Put the picture on one page, say Sheet1.
Copy the picture.
Paste it to another page.
Click on the copied picture, then click into the formula bar and type =Sheet1!$A$1
...Your picture copy is now linked to cell A1 on Sheet1. If, before doing the copying and linking, you make sure that your picture is sitting exactly in the cell(s) on Sheet1 - in this case cell A1 - then it doesn't look too bad. Especially if every time you replace the picture, it is the same size and you can put it into the cell(s) without changing their dimensions. Depending on how you finesse it, the linked pic can be more or less distorted.
Of course, you could probably mess around with your header or footer in order to get the picture to be where you want it... Then you could do page setup for all sheets at the same time, and change out the picture that-a-way.
Schielrn, I tried your suggestion and I don't think you can work with objects while multiple sheets are selected...