There is no custom compression...
On the Picture menu, click Compress Pictures.
Do one of the following:
To compress your pictures for insertion into a document, under Compress for, click
Documents.
To compress your pictures for publication on a Web page, under Compress for, click
Web pages.
To compress your pictures for sending in an e-mail message, under Compress for, click
E-mail messages.
Click OK.
Note You can undo compression by clicking Undo Compress Picture on the Edit menu.
Compression changes will not be saved until you explicitly save them. You can save
your compression changes either immediately after performing them, or at any time
before closing Office Picture Manager.
You can change both file size and picture dimensions by compressing the files to a
smaller JPG format. Microsoft Office Picture Manager automatically determines the
amount of compression after you specify how you intend to use the pictures. The
aspect ratio (aspect ratio: The ratio between picture width and picture height. This
ratio can be maintained even when resizing a picture.) of your pictures will always
be maintained. If your picture is already smaller than the compression option you
have chosen, no resizing or compression will be performed