How do you distinguish cells from one another in the images and do we care about single ones or we just care about the area? Also for cell migration measurement do you measure the empty area with imagej?
Do you consider vibration of the individual cells as an important phenomena for biology or just the progressive movement is of interest?
Cell Migration assay is very well known assay. There are varieties of cell migration assays like Boyden chamber assay, scratch assay, agarose drop assay and cell culture inserts are also available. But you need to be more specific about your cell system, whether it is regarding primary cells or you want to look into the cancer cell invasion (metastasis) etc. Depending on that you can use the cell migration assay.
And in general the migration front is considered in the migration assay. Individual cells can also be examined to study the morphology and all.
2 photon microscopy, Multiphoton microscopy imagine is the coolest way to visualise invivo cell migration, with the many florescent tag available out there, you can looks at how different cells migrate in response to stimulus. But is every expensive assay :0