How are you creating your image sequences?
I deal with animators who give me a long series of images as well as time lapse sequences from cameras such as the Go Pro.
Here’s how I do it.
File > Import.
Browse to the folder these files are in and click on the first image in the sequence.
At the bottom of this window, click the Open still image sequence box.
Make sure the range is correct and click Open.
Set any desired options (such as alpha channel) in the box that comes up and click OK.
The sequence is converted to a file that can be dropped on your Vegas timeline.