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On way to achieve it :

Update the app/design/frontend/{VendorName}/{ThemeName}/etc/view.xml of your theme :

 <image id="product_custom_image" type="image_productlist">
 <width>265</width>
 <height>265</height>
 </image>

You need to update the default configuration file view.xsd as described in this post with a plugin: Extending the complexType named "imageType" with a custom image type

<xs:enumeration value="image_productlist"/>

Then use the default image helper function in order to retrieve your image type such as :

/**
 * @var \Magento\Catalog\Helper\ImageFactory
 */
protected $helperFactory;
$image = $this->helperFactory->create()->init($product, 'product_custom_image')
 ->constrainOnly(true)
 ->keepAspectRatio(true)
 ->keepTransparency(true)
 ->keepFrame(false)
 ->resize(200, 300);
$imageUrl = $image->getUrl();

On way to achieve it :

Update the app/design/frontend/{VendorName}/{ThemeName}/etc/view.xml of your theme :

 <image id="product_custom_image" type="image_productlist">
 <width>265</width>
 <height>265</height>
 </image>

You need to update the default configuration file view.xsd as described in this post with a plugin: Extending the complexType named "imageType" with a custom image type

<xs:enumeration value="image_productlist"/>

Then use the default image helper function in order to retrieve your image type such as :

/**
 * @var \Magento\Catalog\Helper\ImageFactory
 */
protected $helperFactory;
$image = $this->helperFactory->create()->init($product, 'product_custom_image')
 ->constrainOnly(true)
 ->keepAspectRatio(true)
 ->keepTransparency(true)
 ->keepFrame(false)
 ->resize(200, 300);
$imageUrl = $image->getUrl();