Magento 2 : How to get Custom module's 'web' directory path/Get custom module image directory path

Use code below to get module directory path

class CustomModel
{
    /**
     * @var \Magento\Framework\Module\Dir\Reader
     */
    protected $moduleReader;

    /**
     * @param \Magento\Framework\Module\Dir\Reader $moduleReader
     */
    public function __construct(
        \Magento\Framework\Module\Dir\Reader $moduleReader
    ) {
        $this->moduleReader = $moduleReader;
    }

    public function getDirectory()
    {
        $viewDir = $this->moduleReader->getModuleDir(
            \Magento\Framework\Module\Dir::MODULE_VIEW_DIR,
            'Vendor_Module'
        );
        return $viewDir . '/frontend/web/images';
    }
}

but if you need to check content static file I'd recommend you to use this way...

class CustomModel
{
/**
     * @var \Magento\Framework\View\Asset\Repository
     */
    protected $assetRepository;

    /**
     * @param \Magento\Framework\View\Asset\Repository $assetRepository
     */
    public function __construct(
        \Magento\Framework\View\Asset\Repository $assetRepository
    ) {
        $this->assetRepository = $assetRepository;
    }

    public function getMyFilePath()
    {
        $fileId = 'Vendor_Module::images/myimage.png';
        $params = [
            'area' => 'frontend'
        ];
        $asset = $this->assetRepository->createAsset($fileId, $params);
        try {
            return $asset->getSourceFile();
        } catch (\Exception $e) {
            return null;
        }
    }
}

You can also use Magento\Framework\Module\Dir Class to get Directory path of the module:

EXample:

    $objectManager = \Magento\Framework\App\ObjectManager::getInstance();
    $dir = $objectManager->get('Magento\Framework\Module\Dir');
    /*Retrieve full path to a directory of certain type within a module*/
    echo $dir->getDir('Magento_Customer');
    echo $dir->getDir('Magento_Customer','Controller');

Syntax:

    getDir('Module_Name','Directories');                                      
    /*getDir method not allow to read type of module's directory except these*/
    const MODULE_ETC_DIR = 'etc';
    const MODULE_I18N_DIR = 'i18n';
    const MODULE_VIEW_DIR = 'view';
    const MODULE_CONTROLLER_DIR = 'Controller';