Here's 3 options:
1) Convert your raster format picture into vector format DXF and import as a sketch
Several software packages will do this, including some freeware if you search around a
bit.
2) Insert your picture as the ViewPort Background for SolidWorks:
Tools>Options>Colors><select> Image File and specify directory path to picture file
3) With a SolidWorks part or assembly file open, Insert>Customize Menue><check box for "Picture" if not already selected>
Then Insert>Picture><specify directory path to picture file>
You'll need to scale the sketch after tracing the picture. With the sketch active, select all, RMB (Right Mouse Button)>Scale Entities> enter scale and reference point in sidebar.