Unlike Drupal 7, Drupal 6 has no core Image module. You can add image functionality in Drupal 6 by adding either the Image module, or use the Content Creation Kit (CCK) and then couple it with Filefield + Imagefield.

Image module

Creates a node per image and includes a gallery option that works with taxonomy terms for organization. A good choice if you are not using a separate gallery module.

With the Image module you can:

• Create and administer images for your site. Each image is stored as a node, with reduced derivatives of the original generated automatically.
• View image handling messages in Administer >> Settings.
• View lists and add image galleries at Administer >> Content management >> Image galleries.
• Configure image sizes and file directories at Administer >> Site configuration >> Images >> File and sizes

Visit the admin page for the module to create the directory for the images and review other settings. Visit Administer > Site configuration > Image toolkit to set the JPEG image compression.

If you use the Image module further modules packaged with it let you do more with your images:

• The Image gallery module lets you organize and display images in galleries. The list tab allows users to edit existing image gallery names, descriptions, parents and relative position, known as a weight. The add galleries tab allows you to create a new image gallery defining name, description, parent and weight. Support for the Views module is included.
• The Image attach module allows an image to be attached to other nodes: pages, stories, or custom content types. You can specify which derivative size is shown in the node in both teaser and full view, and also the weight of the image among the node's content. The attached image is linked to the node for the actual image, allowing readers to see the full size image. Support for the Views module is included.
• The Image import module allows mass importing of images from a directory on your webserver.
• The ImageMagick Advanced Options module adds advanced ImageMagick options such as image sharpening to the ImageMagick image toolkit.

File issues, read about known bugs, and download the latest version on the Image project page.

Other image handling module

Some image upload modules create a node per image and you can then use the nodes with modules that would not recognize an image. You want simplicity when first loading images, something like Image Picker. Later, after you add image uploading for lots of users and people leave, you want ways to review and organize images, perhaps the gallery included in the Image module. If you have already selected a gallery module or a specific content editor, then you need compatibility with those modules.

Image Assist

http://drupal.org/project/img_assist
Adds on to Image. Connects to TinyMCE via Wysiwyg API. Requires Views module.

Image Browser

http://drupal.org/project/imagebrowser
Adds on to Image. Alternative to Image Assist and IMCE for image browsing. Requires Views module.

Image Picker

http://drupal.org/project/imagepicker
The Image Picker module is an image upload feature modeled after the image upload currently built into Wordpress but with a few improvements.
Could be useful when converting a site from Wordpress. Does not create a node for the image.

Image watermark

http://drupal.org/project/watermark
Adds on to Image. This modules allows a Drupal site running the image module to overlay each image with a watermark. The watermark is a PNG (24 bit) file with an alpha channel, but other formats may work.

IMCE

http://drupal.org/project/imce
Works with FCKEditor, TinyMCE, WYMEditor, and other editors. Has quotas and upload limits you can apply to users when you open the upload floodgate to the whole world.

This module combines the useful bits of Image and Image Assist for adding images to content using just one module and no fancy prerequisites. I selected IMCE for http://ignitesport.net because there are a small number of editors and they each use their own selection of images.

The image is not attached to a node, leaving you without taxonomy categorization and some other features you would use in sites containing many images and many content editors looking for images from a combined library. A site like imdb.com would require categorization by movie, actor, year, etc, and would look for an image node.

Upload Image

http://drupal.org/project/upload_image
upload_image.module takes uploaded images, that are attached to nodes, and creates image nodes from them. Thumbnails are shown in place of the file name in the list of attachments.
The module depends on both upload.module and image.module.

Other modules for handling image in your Drupal site:

• Image Attach Browse: augments Image Attach by adding a thumbnail browser to the "Attached Images" fieldset of the node form.
• Image Gallery Access: control what user roles can view, edit, delete and post to each gallery.
• Image Gallery Management: use thumbnails to assign many images to a selected gallery in one action.
• Image cycle: allow image galleries to be displayed as sideshows using the jquery cycle plugin.
• Image assist: upload and insert images into posts.
• Image Assist Flickr extension: an extension for Image Assist that provides a browsable interface for Flickr images.
• Image Browser: allows you to browse Image nodes from FCKeditor and then insert either Image or ImageCache presets into a node.
• Image FUpload: Upload multiple images with one click.
• Multiple Image Upload: enables images to be "drag 'n' dropped" into Drupal.
• Upload Image: creates Image nodes from attachments, and shows thumbnails in place of the file name.
• ThickBox: a wrapper for the jQuery plugin ThickBox.
• Lightbox2: places images above your current page, not within.
• Views: can be used to display collections of images and other content.
• MAQUM: Metadata Aware Quick Upload Module will process your image's metadata and create your image node using ExifTool.
• Taxonomy Image: allows site administrators to associate images with taxonomy terms.
• Image filter: allows you to use tags of the form [image:nodeid] within node body, referring to the id of an image node.
• Diaporama: allows you to display images in a flash slideshow, by using the Dewslider flash image player.
• Acidfree Albums: An alternate gallery module with per user or shared albums.
• Plupload integration: Upload multiple files to store in a single filefield per node using Plupload library.

Note: whichever method you choose, ensure you don't have an input filter that strips out the html tags that would allow images to be displayed(!)