Do you have a single data region that touches every page?  If you do, I
think selecting the 'Repeat report item with data region on every page' will
do the trick.  If not, I'm not sure that leaving the data region drop down
will do the trick.  Here's what the help says, it isn't specific enough to
answer the question.  Oh, you are talking about the background image
property for the Body.  Yes, the image should repeat for every page in the
report.  I tested it with the following settings.  My test only used one
data region, but with that property shouldn't matter.

<Style>

<BackgroundImage>

<MIMEType>image/png</MIMEType>

<Source>Embedded</Source>

<Value>gradientme</Value>

</BackgroundImage>

</Style>

From Help:
Repeat report item with data region on every page

Choose this option to show the image with a data region each time the data
region appears on a page. This is useful for headings that should appear
with the data region on each page of the report.

Thanks,

Steve MunLeeuw