Most operating systems and web applications sort a set of files based off of their name. Numbers come first (0-9), then letters (A-Z), so a filename Image-1.jpg will come before Image-A.jpg.
When your filenames are not zero-padded, it can cause some unexpected results. Take the following list of filenames, for example:
Since many systems sort by name, these images will sort with Image-1.jpg first, and then Image-10.jpg, followed by Image-11.jpg. This is because the 1 in Image-10.jpg and Image-11.jpg comes before the 2 in Image-2.jpg.
To sort your images as expected, always be sure to zero-pad your filenames when renaming them. So, for example:
When you do this, the 0 will be seen as the first number (for the first nine images), and therefore your images will sort as expected, before getting to Image-10.jpg and Image-11.jpg.
Use a zero-pad that makes sense based on the number of images you have. If you have less than 100 images, then having only one 0 is fine. If you have more than 100 but less than 1000, then having two 0's is fine.
For consistency, we recommend always having three 0's so you don't run into a situation where you would have unexpected sort results (unless you are delivering over 10,000 images in a session).
To zero-pad your filenames in Lightroom:
Select all your images in the Grid view.
Select Library > Rename Photos.
From the "File Naming" dropdown, click "Edit."
Insert Custom Text, type a "-" and then insert Sequence # (0001).
Press "Done" and type in the name you'd like to use as the prefix (i.e. the client's name).