automating photoshop

(ive already posted this on the general forum but thought in hindsight that it might be better off here, sorry i didnt mean to spam!)

automating photoshop
iam trying to write an automation programme that opens photoshop(i can do this), and then watches photoshop and waits till it fulfills a condition before stepping in and playing an action.

specifically my program will wait till an image is 500x500 and then it will play an action

below is the code i have tried, i know i'm thinking to simplistically but if anyone oculd point me in the write direction i would be most grateful.

Private Sub Command1_Click()
Dim PhotoDoc As IAutoPSDoc
Dim App As PhotoshopApplication

Set App = CreateObject("Photoshop.Application")


If ImageSize = 500 Then
App.PlayAction ("140 Action")
End If


End Sub

cheers