A lot of people have been asking about blender and floating panels in the past, apparently 2.4 series had some floating panels, would be nice to have em back, for stuff like this.
or you can use this irfanview, open you image and in the options menu click always on top
this is a nice app it has the capability of batch resizing and renaming images…
Or spend some time creating appropriate image collages with GIMP or similar program.
B.t.w. one of the most critical advices I got about hard surface modeling was a tutorial in which, instead of using a blueprint as is, the different parts were neatly separated into different images, the scale of the parts was carefully unified and the positions carefully coordinated. 15 minutes of design/preparation work which made the rest of the modeling a breeze.