A helper method should be created to centralize which extensions are used for images.

[dan.rossiter]

In keeping with the helper methods introduced in 3.6 for audio/media extensions retrieval, the retrieval of image extensions should similarly be wrapped in a filterable method. Currently all places where this information is needed appear to simply define their own array and use that -- very un-DRY.

[dan.rossiter]

Proposed patch for creating wp_get_image_extensions()

[swissspidy]

FYI there's a typo in the filter DocBlock: An array of support audio formats.. It should be image formats.