You can use Obsidian Embeds to embed an image. In these cases, if you want a specific size for the image, the display text of the internal link can be set to a string specifying the dimensions:

For example, for dimensions of width of 100 and a height of 145:

![[Foobar.jpg|100x145]]

Or, with a width of 100 and a height that keeps the original aspect ratio:

![[Foobar.jpg|100]]

Source: help.obsidian.md