Hi Carrie,
JPEGs can optionally store 'resolution' (i.e. a pixel per inch PPI reference
that some programs can be used to determine the 'intended'
viewing size) [pixels have no set size]. GIF files do not
have the ability to store a PPI value and is nominally
96 PPI.
Hovering your mouse pointer over a graphic in
MS Office Picture Manager will show the width & height in
pixels. Right click on a picture and choose Properties brings
up the Properties task pane (or use View=>Task Pane
and choose the Properties pane in the TaskPane.
Once there click on the 'More...' link
in the 'Picture Properties' section to see the resolution,
if any, saved within the graphic.
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How I look up the resolution of a jpeg or gif file in picture manager? >>
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Let us know if this helped you,
Bob Buckland ?

MS Office System Products MVP
*Courtesy is not expensive and can pay big dividends*
Office 2003 Editions explained
http://www.microsoft.com/uk/office/editions.mspx