IF YOU INTEND TO MAKE PRINTS FOR SALE don't be lured into buying image collections where a large quantity is trumpeted in the headline. You can't beat the law of physics to fit a quart into a pint pot when it comes to good quality large file size images! It can be very expensive to ignore copyright laws also, as many amateur fly by night, on-line sellers commonly do. Here are a few tips:

1. QUANTITY:
 The larger the quantity the less you will get (in quality). Don't be lured into buying large numbers of low quality, tiny size images - they are simply unprintable. Thousands of images on a CD only means wasted money!

2. THE SELLER:
Some image collections offered for sale, such as branded advertising or travel posters, may be still under copyright protection. If a new, unknown seller's description blithely encourages you to start a business selling such prints be very wary - ask.

3. RESTORED?:
 Be sure the antique images have been restored and/or enhanced especially for digital printing. This is an essential task that can make all the difference in a print's saleability or otherwise. If the seller has not already carried out this work it will mean a great deal of extra time for you and affect the viability and the reputation of your business. The lure of a 'cheap' image collection usually means money wasted.

4. SIZE:
 Make sure the supplied images are both a suitable size physically for making prints and also well over the basic 72dpi often supplied. Image pixels are often quoted as a physical dimension but this can be misleading for beginners if they need to compress them themselves to achieve a high enough resolution/physical size ratio for saleable prints (assuming the supplied quality is high enough to begin with). A high dpi resolution is only meaningful if it is accompanied by a large enough physical size too and the original is also of high clarity.
 It is easy to create so called high resolution 300dpi images by reducing poor-resolution images down to small physical sizes or alternatively by expanding the dpi figure artificially with a graphics program (without making an actual difference to the quality of the print) so be wary of dealers using these deceptions which rely on the ignorance of a purchaser.

5. LEGALITY:
Do resist the temptation of lifting images from the internet. Often this is simply theft of another's scan or photo which may be copyrighted, or the image itself may still be under copyright. Remember too that retro style doesn't necessarily mean the work is actually old and public domain. Additionally it may be a substantially restored and/or uniquely enhanced work which, as a significantly improved version of the original is itself subject to automatically renewed copyright protection. Even apparently public domain material shown on museum sites may be protected simply because the scans are another's work (only the original itself is copyright-free, not the scan).
Several museums now employ the use of agents to track illicit usage of its material. We are often told "I found a similar image on Google, why should I buy yours?" Search sites simply trawl for images. Obviously they do NOT check copyright before displaying them and simply warn the user that material may be copyrighted (it often is). It's a minefield that needs to be trod very carefully where the danger is a potential large financial loss through a big damages suite rather than loss of a limb.
Avoid the temptation at all costs. It simply isn't worth the enormous risk, especially when better quality, restored image collections can be had for extremely low cost anyway!