I sandwiched my pcb artwork onto my pcb using a photoframe then placed the frame on top of my leds. I exposed it for like 4mins. I was going to expose for 2 but I over ran abit lol. Anyway bits of it didn't even transfer. When it did transfer I could clearly see the traces but it was faint when I developed it. Admittedly I did staple two copies of my artwork together which meant the artwork wasn't pressed flat aginest the pcb . Does that matter?
You want transparency sheet pressed on PCB as flat as possible, no bubbles or gaps and you want it toner side to PCB. What i mean is you want toner to be as close to UV sensitive coating as possible, otherwise youll get shadows with blury edges.
Overexposure might be a problem too as UV does get thru toner in the long run. I usually lay two copies of a print for one side of PCB (as ideally aligned as possible of course)
Another opposite thing - you mention you are using a photoframe. Does it have a glass or plexiglass in it? UV is filtered out by glass, you need a plexiglass as it's more transparent for UV.
Edit: I usually use two copies of artwork and water - wet transparencies want to stick togeather because of water surface tension. The same for "glueing" it to PCB. It's just a matter of pushing air bubbles from under transparency - i use a couple of cotton balls - one hand to hold board in place and other to swipe bubbles to the sides.