OP; Building on what the other guys have already shown;

- I have often needed to quickly go from a photo to get dimensions (for all sorts of things besides bike frames).

- It has often been simplest to save the photo out as a JPEG file and then insert it into PowerPoint and get busy with it
-- Assuming you have some idea how big the item is in the real world, set the page size to be a bit larger
-- Use a scale of 1 PowerPoint inch or cm on screen (your choice) = 1 foot or 1 inch or 1 cm, real world, as needed
-- Then insert the JPEG file into the blank PowerPoint drawing.

- If you know any dimension of any part of the item in the picture, then make a line that size to compare the JPEG to.
-- Move this line over on top of the picture and position it about where the known part is.
-- If you know the angle of the known part, you can enter that angle into the rotation of the new line
-- Then click once on the picture, and resize it so the known item in the photo is the same size as the new line. Keeping proportions the same when resizing.
-- Zoom in a lot to make sure the starting and end points of the line you made and the known part in the photo are spot on. Resize the photo as needed to get it right.

- After you have the photo the correct size, you can lay other PowerPoint lines, rectangles, circles, etc., over top of it, resize them to match that in the JPEG, and then take your dimensions from them. While not a high precision CADD program, pray tell, PowerPoint can get you close enough for most uses and most folks have it installed on a computer near them. Really handy for sorting out a bicycle ad on ebay where the seller knows only that it has 700C wheels but has one picture of it and no clue as to the seat-tube or top-tube or the chain-stays.

Hope that helps a bit

/K