Some MORE nice work Cyclone (see my post re: your web site for further feedback)
These shots are very good - and I'm saying that as a fellow professional.
A few short comments which you can take or leave as you see fit.
While the macro work on the tin toys is good, I can understand why a stock library would say no to them. Stock libraries know that their most important customer segments would be graphic designers, advertising agencies, magazines, web designers and the like. These people are looking for images that become metaphors or ilustrations of larger concepts ...and right now that's not coming through in your toy images. Take those same tin toys however and surround them with props that all scream \"1940s nostalga\" and I reckon that you'll be able to sell them.
Also, all those toys were framed in the same way - you need to break it up and vary it more with a series of shots like this. With the car for example, get down in front of the car and shoot from there - as if it was about to run you over... (or put the tin bird next to a real one on a white background ...and all of a sudden your series has a bit more interest in it.
The live bird shots are excellent. I know what your friend was getting at with the cropping. What I would do if I were you is crop the images so there is space for copy (words) along side them. With image no. 12 for example, put the bird in the bottom right hand corner instead - or in the middle of a left-side / right-side third ..this leaves plenty of room for me as a graphic designer to add a headline and sub head next to the picture - this creates a nice static layout with plenty of colour and contrast for the eye to wander over. In effect it stops being just a picture of a bird and starts being a masthead of a magazine article on birds, or gardens, or nature, or the environment... and right away you've got four different uses from the same image (and four different sales for the stock library!

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If you can create images that suggest/illustrate a number of larger concepts, while slotting effortlessly into a press / editorial layout with plenty of room for copy, then you're MUCH more likely to sell your images to libraries or agencies.
No disrespect though - it's still all good work. Keep it up!