Image max width or max heigth

[Mohammadshekari]

i suggest to add this attributes: picture = ResizedImageField(max_width=640, max_height=640)

i think its better than quality

[Gagaro]

size is the parameter used for width and height.

Feel free to open a PR to add those. We should not have both size and max_width / max_height passed at the same time.