TYPO3 8.7 LTS - How to enable the image cropping tool in your own extension

People using TYPO3 7.6 or 8.7 for sure know the cool Image Cropping tool that was introduced with TYPO3 7. As an extension developer, you can easily switch on the Image Cropping tool for your own extension by enabling adding the imageoverlayPalette to the foreign_types config array for the FILETYPE_IMAGE in the TCA like shown in this blogpost by Marcus Schwemer. In TYPO3 8.7 the Image Cropping tool does not show as expected, due to structural TCA changes in the TYPO3 8.

For TYPO3 8.7, the following (minimal) TCA configuration will enable the Image Cropping tool for the field "image" in an own extension:

'image' => [
    'exclude' => 1,
    'label' => 'LLL:EXT:custom_extension/Resources/Private/Language/locallang_db.xlf:tx_customextension_domain_model_tablename.custom_field',
    'config' => \TYPO3\CMS\Core\Utility\ExtensionManagementUtility::getFileFieldTCAConfig('image', [
        'foreign_match_fields' => [
            'fieldname' => 'image',
            'tablenames' => 'tx_customextension_domain_model_tablename',
            'table_local' => 'sys_file',
        ],
        'overrideChildTca' => [
            'types' => [
                \TYPO3\CMS\Core\Resource\File::FILETYPE_IMAGE => [
                    'showitem' => '
                            --palette--;LLL:EXT:lang/Resources/Private/Language/locallang_tca.xlf:sys_file_reference.imageoverlayPalette;imageoverlayPalette,
                            --palette--;;filePalette'
                ],
            ],
        ],
        'minitems' => 0,
        'maxitems' => 999,
    ], $GLOBALS['TYPO3_CONF_VARS']['GFX']['imagefile_ext']),
],

Note, that the configuration array only shows the configuration for a single field and that the array must be located in the "columns"-array of your domain model TCA. For TYPO3 8.7, the overrideChildTca config is the important part, which enables the Image Cropping tool.

If your extension needs to support TYPO3 7.6 and 8.7, your TCA should include both the overrideChildTca config as described in this blogpost and the foreign_types config as described in Marcus's blogpost.