django: add form field to generated form from another table
The short answer is yes. You would have to be careful with your template and views. 
Can you please share your code... view, django models and template. Are you using model forms? Why are you keeping them as separate models (tables)? 
My suggestion is if you don't need to keep the models separate, edit the Product model to include Pictures. Then your form will suit your needs nicely.
Hope this helps. If not, share code.
I have this table Products:

size
color
etc
and another table Pictures:
product_id
picture
and I have generated form from Products table, but I also need there field for adding a picture to that product. Is it possible to add a field to the product generated form for a  picture?
Thanks in advance.