REQUIREMENTS
As of version 2.29, on many servers you can automatically thumbnail your images as they are uploaded.

Automatic thumbnailing requires a perl module for ImageMagick (any) or GD (1.26 or later) on your server. If present, Listings Manager will automatically detect the presence of the correct module. Because of this requirement, many users may not be able to use thumbnailing at this time.

GD added the ability to process jpg files with version 1.26 of the GD perl module (or gd.pm). (Note that this is different from the GD library, also known as libgd.) Listings Manager does not use earlier GD versions for image processing.

Some service providers will believe that they have GD or ImageMagick installed, but they do not actually have the Perl Module, rather some other module or library for those products.

Occasionally a module will be detected, but many default functions were not configured by your host for some reason. If Listings Manager reports errors when uploading images, please disable auto thumbnail generation and contact our support team.

THUMBNAILS NOT AVAILABLE

If you see a message of "Thumbnails are not available" it means that your server does not have one of these modules installed - you will need to contact your server administrator or service provider to see if they can assist you. Automatic thumbnailing is an optional feature. If neither modules are available, image thumbnails can still be created by constraining the image height or width within the publish templates.

Note: GD will not thumbnail GIF files, so if both are present ImageMagick will take precedence.

SETTING UP THUMBNAILING
In Setup Options, you'll need to enable automatic thumbnailing, and set the dimensions of the thumbnails. You do not need to set both dimensions - I'd recommend constraining either height or width, but not both.

Placeholders:

$file$ - image filename (used in "image" templatecell)
$thumbnail$ - thumbnail filename (used in "image" templatecell); published the original filename if a thumbnail is not available (as per $file$ above)
$thumbnail_width$ - width of thumbnails (used in "image" templatecell)
$thumbnail_height$ - height of thumbnails (used in "image" templatecell)

You can replace nearly all of your $file$ tags with $thumbnail$. Use $file$ only when you want to display the full sized image - or in the HREF for links to the image itself.

When there is no thumbnail available, Listings Manager will publish the original file in place of the $thumbnail$ tag.

The $thumbnail_width$ and $thumbnail_height$ tags publish the numeric values of the thumbnail height and width set in the Setup Options. You can use these to constrain your images by width="$thumbnail_width$", rather than width="150", for example. These placeholders are available regardless of whether automatic thumbnailing is enabled.