I follow a few of the fashion bloggers that do regular postings of what they wear. A number of them have mentioned how a photo of themselves in their outfits allows them to see what is most flattering in a way that they don't when looking in the mirror. I think the problem with a mirror is that we are often too close to it to properly analyze proportions in the way we can in a photo. After all, most viewers see us from much further back.
Try taking some photographs of yourself in the garments you knit to better understand more about what flatters you so you can improve your next knitting project. I have also read articles written by makeup artists who mention what a big problem this can be with some of their clients. They assess their makeup with a magnifying mirror instead of from 18 inches or more away and are overly critical.
One other thing that you need to be aware of is the problem that most of us don't like to see ourselves in photos. The reason for this is that we’ve always seen ourselves as no one else has, in a mirror. This is the image we have of ourselves in our mind. It is actually a mirror image of what everybody else sees and what a camera captures. The negative reaction is said by perceptual psychologists to come from seeing the many small asymmetries that don’t match up with what our brain expects to see, we then dislike the image. There is a short video talk on this topic here if you would like to know more. It is given by Duncan Davidson who is an author, small-business owner and software developer. He has been the principal photographer for all major TED events since 2009.