WPF: How to display an image at its original size?

Here is a similar question. Generally setting Stretch="None" is enough.

It is also very important what DPI has the image set in metadata. It took me quite a while before figuring out that if the image's DPI is different from the monitor's DPI (usually 96), WPF will automatically resize the image, as it tries to be DPI-independent.

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EDIT

The MSDN link is broken, here is the new link: MSDN Blog - Blurry Bitmaps. Let's keep the old link around to be used for archive.org, in case the new link stops working also.

Try not specifying width or height, use it like this instead:

<Image Source="/images/user_add.png" Stretch="None" HorizontalAlignment="Center" VerticalAlignment="Center" />