I have the same problem, using apache 2.0.55-r3(threads) + mod_perl 2.0.2 + GD + gd.2.0.33 on a amd64. I tried to compile everything again, reintall apache, gd, mod_perl, but the problem persist. The problem is not related with the graphic format: I get it for jpg, png and gif. Did you find any solution?