Function decode_bytes_within 

pub fn decode_bytes_within(
    data: &[u8],
    max_side: u32,
) -> Result<RgbaImage, String>

Decodes the picture in data no larger than max_side pixels on its longer side, as straight-alpha sRGB RGBA, not turned. ImageIO scales while it decodes (a JPEG at a fraction of its size directly), so a huge picture never sits in memory at full size. Any format ImageIO reads.