1. Rename it Create Mosaic, because it can do that too, and a strip of images is just a one-dimensional mosaic.
2.a. Add an option to resize a strip of images. As it stands now, this feature allows you to specify a fixed height of a horizontal strip of images, but if you are constrained by the width, you have to resize the resulting strip manually. The resizing to a specified width could be performed automatically after the strip is created.
2.b. As a more useful alternative to 2.a, in mosaic mode have an option to make the individual images on each row have the same height and variable width (this is how strip mode with specified height behaves), or the option to have the images on each column have the same width and variable height (like the vertical strip mode). As it stands now, the mosaic mode has even width columns and uneven height of rows, which leaves gaps between rows of pictures.
2.c. An even more useful alternative feature would be to be able to manually resize each picture of the mosaic (with the option to keep or discard the original aspect ratio). When you make a picture too big for its spot it would push the neighbouring pictures so that they do not overlap. This would be done in an interactive manner, with the option to snap to the height or width of neighbouring pictures.
I realise 2.c could be complicated to implement, so I am not very hopeful, but 2.a or 2.b should only be reusing already existing features. (I am no programmer, so I apologise if I am saying stupid things
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