CSS: how to vertically and horizontally align an image?

Question

My page has space for an image that can be, say, a maximum 100x100 image. Users can upload any image dimension and the web application will resize it, maintaining aspect rat

Answer 1

I know this is and old question already answered but now you can use flex

CSS

.container {
    display: flex;
    justify-content: center;
    align-items: center;
    border: 1px solid;
    width: 50vw;
    height: 50vw;
}
.container img
{
    max-width:100%;
    max-height:100%;
}

Fiddle Demo

you can also customize the size of your container, some browser may not support flex you can check it here caniuse