It is possible to load png data into Slicer. Specifically for analysis in the BoneTextureExtension you will need to save/export that image into nrrd or other volumetric image formats.
Please provide a bit more of info, and I/the rest of the Slicer community will try to do our best to help.
Best,
HeterogeneityCAD is an extension, not a core module - you will first need to install it using ExtensionManager.
You can also consider looking into the Radiomics extension that provides the Slicer interface to the pyradiomics library, which can be used to calculate ~1500 features: http://pyradiomics.readthedocs.io/en/latest/
The BoneTexture Extension is not able to compute textural features for 2D images, it only can be used for 3D scans in Slicer.
Therefore you can consider using the itk_texturefeatures python package that contain filter able to compute 1st order, Run Length an Co-occurrence textural features and textural feature maps for 2D and 3D images and can easily be intalled: pip install itk_texturefeatures.
The BoneTexture Extension is not able to compute textural features for 2D images, it only can be used for 3D scans in Slicer. But I need to deal with 2D images. Is there any module can compute 2D images?